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Programming:Sin/Cos calculation

2010-02-24T14:15:57Z

Apollo: Updated dead link to CORDIC algorithm

== Calculation using lookup table ==

The calculation is based on a table from 0-90° and on values which are multiplicated by 32767. If you want to get the correct sinus value, you have to divide them by 32767 (you can use 32768 - not a big precision lost, but you can use bit shifting).

'''Input:''' HL = ''angle in degree (0-360°)''

'''Output:''' HL = ''SIN(HL) * 32767'', A = ''sign flag (0 if positive, &FF if negative)''

<pre>
INTSIN: LD BC, 360
LOOP1: BIT 7, H ;angle positive?
JR Z, LOOP2 ;-> yes, ok
ADD HL, BC ;else add 360
JR LOOP1 ;repeat until H>0

LOOP2: OR A ;reset carry
SBC HL, BC ;angle - 360
JR NC, LOOP2 ;->ok if >=0
ADD HL, BC ;else correct value

LD E, L ;angle to DE
LD D, H
LD BC, 90
XOR A ;sign flag = 0
SBC HL, BC ;angle < 90?
JR NC, TEST2 ;-> no
EX DE, HL ;else HL = angle
JR GETTAB ;get table value

TEST2: SBC HL, BC ;angle < 180?
JR NC, TEST3 ;-> no
LD HL, 180 ;else HL =
OR A ;180 - angle
SBC HL, DE
JR GETTAB ;get table value

TEST3: DEC A ;sign flag &FF
SBC HL, BC ;angle < 270?
JR NC, TEST4 ;-> no
EX DE, HL ;else HL =
OR A ;clear carry
SBC HL, BC ;angle - 180
SBC HL, BC
JR GETTAB ;get table value

TEST4: LD HL, 360 ;if angle >=270
SBC HL, DE ;HL = 360 - angle

GETTAB: ADD HL, HL ;angle * 2
LD DE, SINTAB ;+ start table
ADD HL, DE ;= tableaddress
LD E, (HL) ;lowbyte to E
INC HL
LD D, (HL) ;highbyte to D
EX DE, HL ;result to HL
RET

;*****
;Sinustable for angles between 0..90 degrees
;*****
;Values*32767

SINTAB:
DW 0,572,1144,1715,2286
DW 2856,3425,3993,4560,5126
DW 5690,6252,6813,7371,7927
DW 8481,9032,9580,10126,10668
DW 11207,11743,12275,12803,13328
DW 13848,14364,14876,15383,15886
DW 16384,16876,17364,17846,18323
DW 18794,19260,19720,20173,20621
DW 21062,21497,21925,22347,22762
DW 23170,23571,23964,24351,24730
DW 25101,25465,25821,26169,26509
DW 26841,27165,27481,27788,28087
DW 28377,28659,28932,29196,29451
DW 29697,29934,30162,30381,30591
DW 30791,30982,31163,31335,31498
DW 31650,31794,31927,32051,32165
DW 32269,32364,32448,32523,32587
DW 32642,32687,32722,32747,32762
DW 32767
</pre>

== Calculation using the CORDIC algorithm ==

Andre Adrian wrote a paper about how to implement the calculation of sin/cos on Z80 CPUs. You can read the paper and find the implementation on his homepage http://www.andreadrian.de/oldcpu/Z80_number_cruncher.html .
[[Category:Programming]]

Emulators

2010-02-23T05:44:26Z

Apollo:

Emulators

2010-02-23T05:23:50Z

Apollo:

Emulator IDs

2010-02-23T05:19:19Z

Apollo:

Some CPC emulators use Port &FEFE to provide a method to identify a specific CPC emulator. CPC programs could use this ID to detect an emulator and change some of their behaviour (e.g. changing graphic effechts which will not work on an emulator or using special emulator-specific features). Reading from this port returns the Emulator-ID or &FF on the real CPC and on emulators which do not provide this feature.

== List of known Emulator-IDs ==
<pre>- #99: WinCPC
- #A0: JavaCPC
- #C0: C-One Normal
- #C1: C-One Turbo
- #C2: TREX Normal
- #C3: TREX Turbo
- #CE: CPCE
- #FF: Real CPC
</pre>
NOTE: It should be noted that the value #FF is just valid on a bare CPC (not plus!) and any extensions connected can change this!
[[Category:Emulator]] [[Category:Programming]]

Gate Array

2009-02-20T20:51:11Z

Apollo: Rollback as undo swallowed all Prettytables & fixed table "Select pen" bit 4=0

Gate Array

== Introduction ==

The gate array is a specially designed chip exclusively for use in the Amstrad CPC and was designed by Amstrad plc.

In the CPC+ system, the functions of the Gate-Array are integrated into a single [[ASIC]]. When the ASIC is "locked", the extra features are not available and the ASIC operates the same as the Gate-Array in the CPC allowing programs written for the CPC to work on the Plus without modification. The ASIC must be "un-locked" to access the new features.

In the [[KC Compact Computer|KC compact]] system, the functions of the Gate-Array are "emulated" in [[TTL logic]] and by the [[Zilog Z8536 CIO]].

In the "cost-down" version of the CPC6128, the functions of the Gate-Array are integrated into a ASIC.

The Gate Array is described here, as it is in a standard CPC.

''What does it do?''

The Gate Array is responsible for the display (colour palette, resolution, horizontal and vertical sync), interrupt generation and memory arrangement.

== Controlling the Gate Array ==

The gate array is controlled by I/O. The gate array is selected when bit 15 of the I/O port address is set to "0" and bit 14 of the I/O port address is set to "1". The values of the other bits are ignored. However, to avoid conflict with other devices in the system, these bits should be set to "1".

The recommended I/O port address is &7Fxx.

The function to be performed is selected by writing data to the Gate-Array, bit 7 and 6 of the data define the function selected (see table below). It is not possible to read from the Gate-Array.

{|{{Prettytable|width: 700px; font-size: 2em;}}
|''Bit 7''||''Bit 6''||''Function''
|-
|0||0||Select pen
|-
|0||1||Select colour for selected pen
|-
|1||0||Select screen mode, rom configuration and interrupt control
|-
|1||1||Ram Memory Management (note 1)
|-
|}

===== Note =====

This function is not available in the Gate-Array, but is performed by a device at the same I/O port address location. In the CPC464,CPC664 and KC compact, this function is performed in a memory-expansion (e.g. Dk'Tronics 64K Ram Expansion), if this expansion is not present then the function is not available. In the CPC6128, this function is performed by a PAL located on the main PCB, or a memory-expansion. In the 464+ and 6128+ this function is performed by the ASIC or a memory expansion. Please read the document on Ram Management for more information.

==== Pen selection ====

When bit 7 and bit 6 are set to "0", the remaining bits determine which pen is to have its colour changed. When bit 4 is set to "0", bits 3 to 0 define which pen is to be selected. When bit 4 is set to "1", the value contained in bits 3-0 is ignored and the border is selected.

The pen remains selected until another is chosen.

Each mode has a fixed number of pens. Mode 0 has 16 pens, mode 1 has 4 pens and mode 2 has 2 pens.

===== Summary =====

{|{{Prettytable|width: 700px; font-size: 2em;}}
|''Bit''||''Value''||''Function''
|-
|7||0||rowspan=2|Gate Array function "Pen Selection"
|-
|6||0
|-
|5||-||not used
|-
|4||1||Select border
|-
|3||x||rowspan=4|Ignored
|-
|2||x
|-
|1||x
|-
|0||x
|-
|}

{|{{Prettytable|width: 700px; font-size: 2em;}}
|''Bit''||''Value''||''Function''
|-
|7||0||rowspan=2|Gate Array function "Pen Selection"
|-
|6||0
|-
|5||-||not used
|-
|4||0||Select pen
|-
|3||x||rowspan=4|Pen number
|-
|2||x
|-
|1||x
|-
|0||x
|-
|}

==== Colour selection ====

Once the pen has been selected the colour can then be changed. Bits 4 to 0 specify the hardware colour number from the hardware colour palette.

Even though there is provision for 32 colours, only 27 are possible. The remaining colours are duplicates of those already in the colour palette.

===== Summary =====

{|{{Prettytable|width: 700px; font-size: 2em;}}
|''Bit''||''Value''||''Function''
|-
|7||0||rowspan=2|Gate Array function "Colour selection"
|-
|6||1
|-
|5||-||not used
|-
|4||x||rowspan=5|Colour number x
|-
|3||x
|-
|2||x
|-
|1||x
|-
|0||x
|-
|}

==== Hardware colour palette ====

{|{{Prettytable|width: 700px; font-size: 2em;}}
|''Colour Number''||''Colour Name''||''Color''
|-
|0||White||bgcolor="#808080"|
|-
|1||White (note 1)||bgcolor="#808080"|
|-
|2||Sea Green||bgcolor="#00FF80"|
|-
|3||Pastel Yellow||bgcolor="#FFFF50"|
|-
|4||Blue||bgcolor="#000080"|
|-
|5||Purple||bgcolor="#FF0080"|
|-
|6||Cyan||bgcolor="#008080"|
|-
|7||Pink||bgcolor="#FF8080"|
|-
|8||Purple (note 1)||bgcolor="#FF0080"|
|-
|9||Pastel Yellow (note 1)||bgcolor="#FFFF50"|
|-
|10||Bright Yellow||bgcolor="#FFFF80"|
|-
|11||Bright White||bgcolor="#FFFFFF"|
|-
|12||Bright Red||bgcolor="#FF0000"|
|-
|13||Bright Magenta||bgcolor="#FF00FF"|
|-
|14||Orange||bgcolor="#FF8000"|
|-
|15||Pastel Magenta||bgcolor="#FF80FF"|
|-
|16||Blue (note 1)||bgcolor="#000080"|
|-
|17||Sea Green (note 1)||bgcolor="#00FF80"|
|-
|18||Bright Green||bgcolor="#00FF00"|
|-
|19||Bright Cyan||bgcolor="#00FFFF"|
|-
|20||Black||bgcolor="#000000"|
|-
|21||Bright Blue||bgcolor="#0000FF"|
|-
|22||Green||bgcolor="#008000"|
|-
|23||Sky Blue||bgcolor="#0080FF"|
|-
|24||Magenta||bgcolor="#800080"|
|-
|25||Pastel Green||bgcolor="#80FF80"|
|-
|26||Lime||bgcolor="#80FF00"|
|-
|27||Pastel Cyan||bgcolor="#80FFFF"|
|-
|28||Red||bgcolor="#800000"|
|-
|29||Mauve||bgcolor="#8000FF"|
|-
|30||Yellow||bgcolor="#808000"|
|-
|31||Pastel Blue||bgcolor="#8080FF"|
|-
|}

===== Notes =====

This is not an official colour

Select screen mode and rom configuration

This is a general purpose register responsible for the screen mode and the rom configuration.

==== Screen mode selection ====

The function of bits 1 and 0 is to define the screen mode. The settings for bits 1 and 0 and the corresponding screen mode are given in the table below.

{|{{Prettytable|width: 700px; font-size: 2em;}}
|''Bit 1''||''Bit 0''||''Screen mode''
|-
|0||0||Mode 0, 160x200 resolution, 16 colours
|-
|0||1||Mode 1, 320x200 resolution, 4 colours
|-
|1||0||Mode 2, 640x200 resolution, 2 colours
|-
|1||1||Mode 3, 160x200 resolution, 4 colours (note 1)
|-
|}

This mode is not official. From the combinations possible, we can see that 4 modes can be defined, although the Amstrad only has 3. Mode 3 is similar to mode 0, because it has the same resolution, but it is limited to only 4 colours.

Mode changing is synchronised with HSYNC. If the mode is changed, it will take effect from the next HSYNC.

==== Rom configuration selection ====

Bit 2 is used to enable or disable the lower rom area. The lower rom area occupies memory addressess &0000-&3fff and is used to access the operating system rom. When the lower rom area is is enabled, reading from &0000-&3FFF will return data in the rom. When a value is written to &0000-&3FFF, it will be written to the ram underneath the rom. When it is disabled, data read from &0000-&3FFF will return the data in the ram.

Similarly, bit 3 controls enabling or disabling of the upper rom area. The upper rom area occupies memory addressess &C000-&FFFF and is BASIC or any expansion roms which may be plugged into a rom board/box. See the document on upper rom selection for more details. When the upper rom area enabled, reading from &c000-&ffff, will return data in the rom. When data is written to &c000-&FFFF, it will be written to the ram at the same address as the rom. When the upper rom area is disabled, and data is read from &c000-&ffff the data returned will be the data in the ram.

Bit 4 controls the interrupt generation. It can be used to delay interrupts. See the document on interrupt generation for more information.

===== Summary =====

{|{{Prettytable|width: 700px; font-size: 2em;}}
|''Bit''||''Value''||''Function''
|-
|7||0||rowspan=2|Gate Array function
|-
|6||1
|-
|5||-||not used
|-
|4||x||Interrupt generation control
|-
|3||x||
*1 Upper rom area disable
*0 Upper rom area enable
|-
|2||x||
*1 Lower rom area disable
*0 Lower rom area enable
|-
|1||x||rowspan=2|Mode slection
|-
|0||x
|-
|}

== Programming the Gate Array - Examples ==

Defining the colours, Setting pen 0 to Bright White.

<pre>
LD BC,7F00 ;Gate Array port
LD A,%00000000+0 ;Pen number (and Gate Array function)
OUT (C),A ;Send pen number
LD A,%01000000+11 ;Pen colour (and Gate Array function)
OUT (C),A ;Send it
RET

Setting the mode and rom configuration,
Mode 2, upper and lower rom disabled.

LD BC,7F00 ;Gate array port
LD A,%10000000+%00001110 ;Mode and rom selection (and Gate Array function)
OUT (C),A ;Send it
RET
</pre>

==== Conversion chart ====

The hardware colour number is different to the colour range used by the firmware, so a conversion chart is provided for the corresponding firmware/hardware colour values and the corresponding colour name.

===== Note =====

The firmware keeps track of the colours it is using. Every VSYNC (assuming interrupts are enabled) the firmware sets the colours. This enables the user to have flashing colours. If the user selects a new colour using the gate array, the new colour will flash temporarily and then return to it's original colour. This is due to the firmware re- setting the colour. When using the firmware, use it's routines to select the colour, and the colour will remain.

{|{{Prettytable|width: 700px; font-size: 2em;}}
|''Firmware Colour Number''||''Colour Name''||''Hardware Number''||''Quick reference colour value''||''Color''
|-
|0||Black||20||&54||bgcolor="#000000"|
|-
|1||Blue||4||&44||bgcolor="#000080"|
|-
|2||Bright Blue||21||&55||bgcolor="#0000FF"|
|-
|3||Red||28||&5C||bgcolor="#800000"|
|-
|4||Magenta||24||&58||bgcolor="#800080"|
|-
|5||Mauve|| 29||&5D||bgcolor="#8000FF"|
|-
|6||Bright Red||12||&4C||bgcolor="#FF0000"|
|-
|7||Purple|| 5||&45||bgcolor="#FF0080"|
|-
|8||Bright Magenta||13||&4D||bgcolor="#FF00FF"|
|-
|9||Green||22||&56||bgcolor="#008000"|
|-
|10||Cyan||6||&46||bgcolor="#008080"|
|-
|11||Sky Blue||23||&57||bgcolor="#0080FF"|
|-
|12||Yellow||30||&5E||bgcolor="#808000"|
|-
|13||White||0||&40||bgcolor="#808080"|
|-
|14||Pastel Blue||31||&5F||bgcolor="#8080FF"|
|-
|15||Orange||14||&4E||bgcolor="#FF8000"|
|-
|16||Pink||7||&47||bgcolor="#FF8080"|
|-
|17||Pastel Magenta||15||&4F||bgcolor="#FF80FF"|
|-
|18||Bright Green||18||&52||bgcolor="#00FF00"|
|-
|19||Sea Green||2||&42bgcolor="#00FF80"|
|-
|20||Bright Cyan||19||&53||bgcolor="#00FFFF"|
|-
|21||Lime||26||&5A||bgcolor="#80FF00"|
|-
|22||Pastel Green||25||&59||bgcolor="#80FF80"|
|-
|23||Pastel Cyan||27||&5B||bgcolor="#80FFFF"|
|-
|24||Bright Yellow||10||&4A||bgcolor="#FFFF80"|
|-
|25||Pastel Yellow||3||&43||bgcolor="#FFFF80"|
|-
|26||Bright White||11||&4B||bgcolor="#FFFFFF"|
|-
|}

This chart also gives a quick reference guide for programming the colours. The number is the colour number which can be sent directly, once the pen has been selected, to get the colour wanted.

Example:

<pre>
ld bc,7f00+1 ;Gate array function (set pen)
;and pen number
out (c),c
ld bc,7f00 ;41
;Gate array function (set colour)
;and colour number
out (c),c
ret
</pre>

==== Pallette R,G,B definitions ====

There are 27 colours which are generated from red, green and blue mixed in different quantities. There are 3 levels of red, 3 levels of green and 3 levels of blue, and these can be thought of as off/no colour, half-on/half-colour, and on/full-colour.

To display a CPC image you will need to use a analogue monitor with a composite sync.

This table shows the relationship between hardware colour number, colour name and RGB mixing.

{|{{Prettytable|width: 700px; font-size: 2em;}}
|''Hardware Colour Index''||''Colour Name''||''R %''||''G %''||''B %''||''Color''
|-
|0||White||align="right"|50||align="right"|50||align="right"|50||bgcolor="#808080"|
|-
|1||White||align="right"|50||align="right"|50||align="right"|50||bgcolor="#808080"|
|-
|2||Sea Green||align="right"|0||align="right"|100||align="right"|50||bgcolor="#00FF80"|
|-
|3||Pastel Yellow||align="right"|100||align="right"|100||align="right"|50||bgcolor="#FFFF80"|
|-
|4||Blue||align="right"|0||align="right"|0||align="right"|50||bgcolor="#000080"|
|-
|5||Purple||align="right"|100||align="right"|0||align="right"|50||bgcolor="#FF0080"|
|-
|6||Cyan||align="right"|0||align="right"|50||align="right"|50||bgcolor="#008080"|
|-
|7||Pink||align="right"|100||align="right"|50||align="right"|50||bgcolor="#FF8080"|
|-
|8||Purple||align="right"|100||align="right"|0||align="right"|50||bgcolor="#FF0080"|
|-
|9||Pastel Yellow||align="right"|100||align="right"|100||align="right"|50||bgcolor="#FFFF80"|
|-
|10||Bright Yellow||align="right"|100||align="right"|100||align="right"|0||bgcolor="#FFFF00"|
|-
|11||Bright White||align="right"|100||align="right"|100||align="right"|100||bgcolor="#FFFFFF"|
|-
|12||Bright Red||align="right"|100||align="right"|0||align="right"|0||bgcolor="#FF0000"|
|-
|13||Bright Magenta||align="right"|100||align="right"|0||align="right"|100||bgcolor="#FF00FF"|
|-
|14||Orange||align="right"|100||align="right"|50||align="right"|0||bgcolor="#FF8000"|
|-
|15||Pastel Magenta||align="right"|100||align="right"|50||align="right"|100||bgcolor="#FF80FF"|
|-
|16||Blue||align="right"|0||align="right"|0||align="right"|50||bgcolor="#000080"|
|-
|17||Sea Green||align="right"|0||align="right"|100||align="right"|50||bgcolor="#00FF80"|
|-
|18||Bright Green||align="right"|0||align="right"|100||align="right"|0||bgcolor="#00FF00"|
|-
|19||Bright Cyan||align="right"|0||align="right"|100||align="right"|100||bgcolor="#00FFFF"|
|-
|20||Black||align="right"|0||align="right"|0||align="right"|0||bgcolor="#000000"|
|-
|21||Bright Blue||align="right"|0||align="right"|0||align="right"|100||bgcolor="#0000FF"|
|-
|22||Green||align="right"|0||align="right"|50||align="right"|0||bgcolor="#008000"|
|-
|23||Sky Blue||align="right"|0||align="right"|50||align="right"|100||bgcolor="#0080FF"|
|-
|24||Magenta||align="right"|50||align="right"|0||align="right"|50||bgcolor="#800080"|
|-
|25||Pastel Green||align="right"|50||align="right"|100||align="right"|50||bgcolor="#80FF80"|
|-
|26||Lime||align="right"|50||align="right"|100||align="right"|0||bgcolor="#80FF00"|
|-
|27||Pastel Cyan||align="right"|50||align="right"|100||align="right"|100||bgcolor="#80FFFF"|
|-
|28||Red||align="right"|50||align="right"|0||align="right"|0||bgcolor="#800000"|
|-
|29||Mauve||align="right"|50||align="right"|0||align="right"|100||bgcolor="#8000FF"|
|-
|30||Yellow||align="right"|50||align="right"|50||align="right"|0||bgcolor="#808000"|
|-
|31||Pastel Blue||align="right"|50||align="right"|50||align="right"|100||bgcolor="#8080FF"|
|-
|}

==== RGB assignments for the software colours ====

This is simply a sidenote to illustrate a pattern in the RGB assignments of the software colours and to show how their value is calculated.

{|{{Prettytable|width: 700px; font-size: 2em;}}
|''Firmware Colour Number''||''Colour Name''||''R %''||''G %''||''B %''||''Color''
|-
|0||Black||0||0||0||bgcolor="#000000"|
|-
|1||Blue||0||0||50||bgcolor="#000080"|
|-
|2||Bright Blue||0||0||100||bgcolor="#0000FF"|
|-
|3||Red||50||0||0||bgcolor="#800000"|
|-
|4||Magenta||50||0||50||bgcolor="#800080"|
|-
|5||Mauve||50||0||100||bgcolor="#8000FF"|
|-
|6||Bright Red||100||0||0||bgcolor="#FF0000"|
|-
|7||Purple||100||0||50||bgcolor="#FF0080"|
|-
|8||Bright Magenta||100||0||100||bgcolor="#FF00FF"|
|-
|9||Green||0||50||0||bgcolor="#008000"|
|-
|10||Cyan||0||50||50||bgcolor="#008080"|
|-
|11||Sky Blue||0||50||100||bgcolor="#0080FF"|
|-
|12||Yellow||50||50||0||bgcolor="#808000"|
|-
|13||White||50||50||50||bgcolor="#808080"|
|-
|14||Pastel Blue||50||50||100||bgcolor="#8080FF"|
|-
|15||Orange||100||50||0||bgcolor="#FF8000"|
|-
|16||Pink||100||50||50||bgcolor="#FF8080"|
|-
|17||Pastel Magenta||100||50||100||bgcolor="#FF80FF"|
|-
|18||Bright Green||0||100||0||bgcolor="#00FF00"|
|-
|19||Sea Green||0||100||50||bgcolor="#00FF80"|
|-
|20||Bright Cyan||0||100||100||bgcolor="#00FFFF"|
|-
|21||Lime||50||100||0||bgcolor="#80FF00"|
|-
|22||Pastel Green||50||100||50||bgcolor="#80FF80"|
|-
|23||Pastel Cyan||50||100||100||bgcolor="#80FFFF"|
|-
|24||Bright Yellow||100||100||0||bgcolor="#FFFF00"|
|-
|25||Pastel Yellow||100||100||50||bgcolor="#FFFF80"|
|-
|26||Bright White||100||100||100||bgcolor="#FFFFFF"|
|-
|}

===== To calculate the colour value =====

'''Red'''

0% => do not add anything

50% => add 3

100% => add 6

'''Green'''

0% => do not add anything

50% => add 9

100% => add 18

'''Blue'''

0% => do not add anything

50% => add 1

100% => add 2

Green Screen Colours

On a green screen (where all colours are shades of green), the colours (in the software/firmware colours), are in order of increasing intensity. So that black is very dark, and white is bright green, and colour 13 is a medium green. (Thanks to [[Mark Rison]] for this information)

[[Category:Hardware]]

Gate Array

2009-02-20T20:37:26Z

Apollo: Undo revision 29782 as Prettytables were destroyed

Gate Array

== Introduction ==

The gate array is a specially designed chip exclusively for use in the Amstrad CPC and was designed by Amstrad plc.

In the CPC+ system, the functions of the Gate-Array are integrated into a single [[ASIC|ASIC]]. When the ASIC is "locked", the extra features are not available and the ASIC operates the same as the Gate-Array in the CPC allowing programs written for the CPC to work on the Plus without modification. The ASIC must be "un-locked" to access the new features.

In the [[KC Compact Computer|KC compact]] system, the functions of the Gate-Array are "emulated" in [[TTL logic|TTL logic]] and by the [[Zilog Z8536 CIO|Zilog Z8536 CIO]].

In the "cost-down" version of the CPC6128, the functions of the Gate-Array are integrated into a ASIC.

The Gate Array is described here, as it is in a standard CPC.

''What does it do?''

The Gate Array is responsible for the display (colour palette, resolution, horizontal and vertical sync), interrupt generation and memory arrangement.

== Controlling the Gate Array ==

The gate array is controlled by I/O. The gate array is selected when bit 15 of the I/O port address is set to "0" and bit 14 of the I/O port address is set to "1". The values of the other bits are ignored. However, to avoid conflict with other devices in the system, these bits should be set to "1".

The recommended I/O port address is &7Fxx.

The function to be performed is selected by writing data to the Gate-Array, bit 7 and 6 of the data define the function selected (see table below). It is not possible to read from the Gate-Array.

{|
|-
| ''Bit 7''
| ''Bit 6''
| ''Function''
|-
| 0
| 0
| Select pen
|-
| 0
| 1
| Select colour for selected pen
|-
| 1
| 0
| Select screen mode, rom configuration and interrupt control
|-
| 1
| 1
| Ram Memory Management (note 1)
|}

===== Note =====

This function is not available in the Gate-Array, but is performed by a device at the same I/O port address location. In the CPC464,CPC664 and KC compact, this function is performed in a memory-expansion (e.g. Dk'Tronics 64K Ram Expansion), if this expansion is not present then the function is not available. In the CPC6128, this function is performed by a PAL located on the main PCB, or a memory-expansion. In the 464+ and 6128+ this function is performed by the ASIC or a memory expansion. Please read the document on Ram Management for more information.

==== Pen selection ====

When bit 7 and bit 6 are set to "0", the remaining bits determine which pen is to have its colour changed. When bit 4 is set to "0", bits 3 to 0 define which pen is to be selected. When bit 4 is set to "1", the value contained in bits 3-0 is ignored and the border is selected.

The pen remains selected until another is chosen.

Each mode has a fixed number of pens. Mode 0 has 16 pens, mode 1 has 4 pens and mode 2 has 2 pens.

===== Summary =====

{|
|-
| ''Bit''
| ''Value''
| ''Function''
|-
| 7
| 0
| rowspan="2" | Gate Array function "Pen Selection"
|-
| 6
| 0
|-
| 5
| -
| not used
|-
| 4
| 1
| Select border
|-
| 3
| x
| rowspan="4" | Ignored
|-
| 2
| x
|-
| 1
| x
|-
| 0
| x
|}

 

{|
|-
| ''Bit''
| ''Value''
| ''Function''
|-
| 7
| 0
| rowspan="2" | Gate Array function "Pen Selection"
|-
| 6
| 0
|-
| 5
| -
| not used
|-
| 4
| 1
| Select pen
|-
| 3
| x
| rowspan="4" | Pen number
|-
| 2
| x
|-
| 1
| x
|-
| 0
| x
|}

==== Colour selection ====

Once the pen has been selected the colour can then be changed. Bits 4 to 0 specify the hardware colour number from the hardware colour palette.

Even though there is provision for 32 colours, only 27 are possible. The remaining colours are duplicates of those already in the colour palette.

===== Summary =====

{|
|-
| ''Bit''
| ''Value''
| ''Function''
|-
| 7
| 0
| rowspan="2" | Gate Array function "Colour selection"
|-
| 6
| 1
|-
| 5
| -
| not used
|-
| 4
| x
| rowspan="5" | Colour number x
|-
| 3
| x
|-
| 2
| x
|-
| 1
| x
|-
| 0
| x
|}

==== Hardware colour palette ====

{|
|-
| ''Colour Number''
| ''Colour Name''
| ''Color''
|-
| 0
| White
| bgcolor="#808080" |
|-
| 1
| White (note 1)
| bgcolor="#808080" |
|-
| 2
| Sea Green
| bgcolor="#00ff80" |
|-
| 3
| Pastel Yellow
| bgcolor="#ffff50" |
|-
| 4
| Blue
| bgcolor="#000080" |
|-
| 5
| Purple
| bgcolor="#ff0080" |
|-
| 6
| Cyan
| bgcolor="#008080" |
|-
| 7
| Pink
| bgcolor="#ff8080" |
|-
| 8
| Purple (note 1)
| bgcolor="#ff0080" |
|-
| 9
| Pastel Yellow (note 1)
| bgcolor="#ffff50" |
|-
| 10
| Bright Yellow
| bgcolor="#ffff80" |
|-
| 11
| Bright White
| bgcolor="#ffffff" |
|-
| 12
| Bright Red
| bgcolor="#ff0000" |
|-
| 13
| Bright Magenta
| bgcolor="#ff00ff" |
|-
| 14
| Orange
| bgcolor="#ff8000" |
|-
| 15
| Pastel Magenta
| bgcolor="#ff80ff" |
|-
| 16
| Blue (note 1)
| bgcolor="#000080" |
|-
| 17
| Sea Green (note 1)
| bgcolor="#00ff80" |
|-
| 18
| Bright Green
| bgcolor="#00ff00" |
|-
| 19
| Bright Cyan
| bgcolor="#00ffff" |
|-
| 20
| Black
| bgcolor="#000000" |
|-
| 21
| Bright Blue
| bgcolor="#0000ff" |
|-
| 22
| Green
| bgcolor="#008000" |
|-
| 23
| Sky Blue
| bgcolor="#0080ff" |
|-
| 24
| Magenta
| bgcolor="#800080" |
|-
| 25
| Pastel Green
| bgcolor="#80ff80" |
|-
| 26
| Lime
| bgcolor="#80ff00" |
|-
| 27
| Pastel Cyan
| bgcolor="#80ffff" |
|-
| 28
| Red
| bgcolor="#800000" |
|-
| 29
| Mauve
| bgcolor="#8000ff" |
|-
| 30
| Yellow
| bgcolor="#808000" |
|-
| 31
| Pastel Blue
| bgcolor="#8080ff" |
|}

===== Notes =====

This is not an official colour

Select screen mode and rom configuration

This is a general purpose register responsible for the screen mode and the rom configuration.

==== Screen mode selection ====

The function of bits 1 and 0 is to define the screen mode. The settings for bits 1 and 0 and the corresponding screen mode are given in the table below.

{|
|-
| ''Bit 1''
| ''Bit 0''
| ''Screen mode''
|-
| 0
| 0
| Mode 0, 160x200 resolution, 16 colours
|-
| 0
| 1
| Mode 1, 320x200 resolution, 4 colours
|-
| 1
| 0
| Mode 2, 640x200 resolution, 2 colours
|-
| 1
| 1
| Mode 3, 160x200 resolution, 4 colours (note 1)
|}

This mode is not official. From the combinations possible, we can see that 4 modes can be defined, although the Amstrad only has 3. Mode 3 is similar to mode 0, because it has the same resolution, but it is limited to only 4 colours.

Mode changing is synchronised with HSYNC. If the mode is changed, it will take effect from the next HSYNC.

==== Rom configuration selection ====

Bit 2 is used to enable or disable the lower rom area. The lower rom area occupies memory addressess &0000-&3fff and is used to access the operating system rom. When the lower rom area is is enabled, reading from &0000-&3FFF will return data in the rom. When a value is written to &0000-&3FFF, it will be written to the ram underneath the rom. When it is disabled, data read from &0000-&3FFF will return the data in the ram.

Similarly, bit 3 controls enabling or disabling of the upper rom area. The upper rom area occupies memory addressess &C000-&FFFF and is BASIC or any expansion roms which may be plugged into a rom board/box. See the document on upper rom selection for more details. When the upper rom area enabled, reading from &c000-&ffff, will return data in the rom. When data is written to &c000-&FFFF, it will be written to the ram at the same address as the rom. When the upper rom area is disabled, and data is read from &c000-&ffff the data returned will be the data in the ram.

Bit 4 controls the interrupt generation. It can be used to delay interrupts. See the document on interrupt generation for more information.

===== Summary =====

{|
|-
| ''Bit''
| ''Value''
| ''Function''
|-
| 7
| 0
| rowspan="2" | Gate Array function
|-
| 6
| 1
|-
| 5
| -
| not used
|-
| 4
| x
| Interrupt generation control
|-
| 3
| x
|
*1 Upper rom area disable
*0 Upper rom area enable

|-
| 2
| x
|
*1 Lower rom area disable
*0 Lower rom area enable

|-
| 1
| x
| rowspan="2" | Mode slection
|-
| 0
| x
|}

== Programming the Gate Array - Examples ==

Defining the colours, Setting pen 0 to Bright White.
<pre>LD BC,7F00 ;Gate Array port
LD A,%00000000+0 ;Pen number (and Gate Array function)
OUT (C),A ;Send pen number
LD A,%01000000+11 ;Pen colour (and Gate Array function)
OUT (C),A ;Send it
RET

Setting the mode and rom configuration,
Mode 2, upper and lower rom disabled.

LD BC,7F00 ;Gate array port
LD A,%10000000+%00001110 ;Mode and rom selection (and Gate Array function)
OUT (C),A ;Send it
RET
</pre>
==== Conversion chart ====

The hardware colour number is different to the colour range used by the firmware, so a conversion chart is provided for the corresponding firmware/hardware colour values and the corresponding colour name.

===== Note =====

The firmware keeps track of the colours it is using. Every VSYNC (assuming interrupts are enabled) the firmware sets the colours. This enables the user to have flashing colours. If the user selects a new colour using the gate array, the new colour will flash temporarily and then return to it's original colour. This is due to the firmware re- setting the colour. When using the firmware, use it's routines to select the colour, and the colour will remain.

{|
|-
| ''Firmware Colour Number''
| ''Colour Name''
| ''Hardware Number''
| ''Quick reference colour value''
| ''Color''
|-
| 0
| Black
| 20
| &54
| bgcolor="#000000" |
|-
| 1
| Blue
| 4
| &44
| bgcolor="#000080" |
|-
| 2
| Bright Blue
| 21
| &55
| bgcolor="#0000ff" |
|-
| 3
| Red
| 28
| &5C
| bgcolor="#800000" |
|-
| 4
| Magenta
| 24
| &58
| bgcolor="#800080" |
|-
| 5
| Mauve
| 29
| &5D
| bgcolor="#8000ff" |
|-
| 6
| Bright Red
| 12
| &4C
| bgcolor="#ff0000" |
|-
| 7
| Purple
| 5
| &45
| bgcolor="#ff0080" |
|-
| 8
| Bright Magenta
| 13
| &4D
| bgcolor="#ff00ff" |
|-
| 9
| Green
| 22
| &56
| bgcolor="#008000" |
|-
| 10
| Cyan
| 6
| &46
| bgcolor="#008080" |
|-
| 11
| Sky Blue
| 23
| &57
| bgcolor="#0080ff" |
|-
| 12
| Yellow
| 30
| &5E
| bgcolor="#808000" |
|-
| 13
| White
| 0
| &40
| bgcolor="#808080" |
|-
| 14
| Pastel Blue
| 31
| &5F
| bgcolor="#8080ff" |
|-
| 15
| Orange
| 14
| &4E
| bgcolor="#ff8000" |
|-
| 16
| Pink
| 7
| &47
| bgcolor="#ff8080" |
|-
| 17
| Pastel Magenta
| 15
| &4F
| bgcolor="#ff80ff" |
|-
| 18
| Bright Green
| 18
| &52
| bgcolor="#00ff00" |
|-
| 19
| Sea Green
| 2
|
|-
| 20
| Bright Cyan
| 19
| &53
| bgcolor="#00ffff" |
|-
| 21
| Lime
| 26
| &5A
| bgcolor="#80ff00" |
|-
| 22
| Pastel Green
| 25
| &59
| bgcolor="#80ff80" |
|-
| 23
| Pastel Cyan
| 27
| &5B
| bgcolor="#80ffff" |
|-
| 24
| Bright Yellow
| 10
| &4A
| bgcolor="#ffff80" |
|-
| 25
| Pastel Yellow
| 3
| &43
| bgcolor="#ffff80" |
|-
| 26
| Bright White
| 11
| &4B
| bgcolor="#ffffff" |
|}

This chart also gives a quick reference guide for programming the colours. The number is the colour number which can be sent directly, once the pen has been selected, to get the colour wanted.

Example:
<pre>ld bc,7f00+1 ;Gate array function (set pen)
;and pen number
out (c),c
ld bc,7f00 ;41
;Gate array function (set colour)
;and colour number
out (c),c
ret
</pre>
==== Pallette R,G,B definitions ====

There are 27 colours which are generated from red, green and blue mixed in different quantities. There are 3 levels of red, 3 levels of green and 3 levels of blue, and these can be thought of as off/no colour, half-on/half-colour, and on/full-colour.

To display a CPC image you will need to use a analogue monitor with a composite sync.

This table shows the relationship between hardware colour number, colour name and RGB mixing.

 

{|
|-
| ''Hardware Colour Index''
| ''Colour Name''
| ''R %''
| ''G %''
| ''B %''
| ''Color''
|-
| 0
| White
| align="right" | 50
| align="right" | 50
| align="right" | 50
| bgcolor="#808080" |
|-
| 1
| White
| align="right" | 50
| align="right" | 50
| align="right" | 50
| bgcolor="#808080" |
|-
| 2
| Sea Green
| align="right" | 0
| align="right" | 100
| align="right" | 50
| bgcolor="#00ff80" |
|-
| 3
| Pastel Yellow
| align="right" | 100
| align="right" | 100
| align="right" | 50
| bgcolor="#ffff80" |
|-
| 4
| Blue
| align="right" | 0
| align="right" | 0
| align="right" | 50
| bgcolor="#000080" |
|-
| 5
| Purple
| align="right" | 100
| align="right" | 0
| align="right" | 50
| bgcolor="#ff0080" |
|-
| 6
| Cyan
| align="right" | 0
| align="right" | 50
| align="right" | 50
| bgcolor="#008080" |
|-
| 7
| Pink
| align="right" | 100
| align="right" | 50
| align="right" | 50
| bgcolor="#ff8080" |
|-
| 8
| Purple
| align="right" | 100
| align="right" | 0
| align="right" | 50
| bgcolor="#ff0080" |
|-
| 9
| Pastel Yellow
| align="right" | 100
| align="right" | 100
| align="right" | 50
| bgcolor="#ffff80" |
|-
| 10
| Bright Yellow
| align="right" | 100
| align="right" | 100
| align="right" | 0
| bgcolor="#ffff00" |
|-
| 11
| Bright White
| align="right" | 100
| align="right" | 100
| align="right" | 100
| bgcolor="#ffffff" |
|-
| 12
| Bright Red
| align="right" | 100
| align="right" | 0
| align="right" | 0
| bgcolor="#ff0000" |
|-
| 13
| Bright Magenta
| align="right" | 100
| align="right" | 0
| align="right" | 100
| bgcolor="#ff00ff" |
|-
| 14
| Orange
| align="right" | 100
| align="right" | 50
| align="right" | 0
| bgcolor="#ff8000" |
|-
| 15
| Pastel Magenta
| align="right" | 100
| align="right" | 50
| align="right" | 100
| bgcolor="#ff80ff" |
|-
| 16
| Blue
| align="right" | 0
| align="right" | 0
| align="right" | 50
| bgcolor="#000080" |
|-
| 17
| Sea Green
| align="right" | 0
| align="right" | 100
| align="right" | 50
| bgcolor="#00ff80" |
|-
| 18
| Bright Green
| align="right" | 0
| align="right" | 100
| align="right" | 0
| bgcolor="#00ff00" |
|-
| 19
| Bright Cyan
| align="right" | 0
| align="right" | 100
| align="right" | 100
| bgcolor="#00ffff" |
|-
| 20
| Black
| align="right" | 0
| align="right" | 0
| align="right" | 0
| bgcolor="#000000" |
|-
| 21
| Bright Blue
| align="right" | 0
| align="right" | 0
| align="right" | 100
| bgcolor="#0000ff" |
|-
| 22
| Green
| align="right" | 0
| align="right" | 50
| align="right" | 0
| bgcolor="#008000" |
|-
| 23
| Sky Blue
| align="right" | 0
| align="right" | 50
| align="right" | 100
| bgcolor="#0080ff" |
|-
| 24
| Magenta
| align="right" | 50
| align="right" | 0
| align="right" | 50
| bgcolor="#800080" |
|-
| 25
| Pastel Green
| align="right" | 50
| align="right" | 100
| align="right" | 50
| bgcolor="#80ff80" |
|-
| 26
| Lime
| align="right" | 50
| align="right" | 100
| align="right" | 0
| bgcolor="#80ff00" |
|-
| 27
| Pastel Cyan
| align="right" | 50
| align="right" | 100
| align="right" | 100
| bgcolor="#80ffff" |
|-
| 28
| Red
| align="right" | 50
| align="right" | 0
| align="right" | 0
| bgcolor="#800000" |
|-
| 29
| Mauve
| align="right" | 50
| align="right" | 0
| align="right" | 100
| bgcolor="#8000ff" |
|-
| 30
| Yellow
| align="right" | 50
| align="right" | 50
| align="right" | 0
| bgcolor="#808000" |
|-
| 31
| Pastel Blue
| align="right" | 50
| align="right" | 50
| align="right" | 100
| bgcolor="#8080ff" |
|}

==== RGB assignments for the software colours ====

This is simply a sidenote to illustrate a pattern in the RGB assignments of the software colours and to show how their value is calculated.

{|
|-
| ''Firmware Colour Number''
| ''Colour Name''
| ''R %''
| ''G %''
| ''B %''
| ''Color''
|-
| 0
| Black
| 0
| 0
| 0
| bgcolor="#000000" |
|-
| 1
| Blue
| 0
| 0
| 50
| bgcolor="#000080" |
|-
| 2
| Bright Blue
| 0
| 0
| 100
| bgcolor="#0000ff" |
|-
| 3
| Red
| 50
| 0
| 0
| bgcolor="#800000" |
|-
| 4
| Magenta
| 50
| 0
| 50
| bgcolor="#800080" |
|-
| 5
| Mauve
| 50
| 0
| 100
| bgcolor="#8000ff" |
|-
| 6
| Bright Red
| 100
| 0
| 0
| bgcolor="#ff0000" |
|-
| 7
| Purple
| 100
| 0
| 50
| bgcolor="#ff0080" |
|-
| 8
| Bright Magenta
| 100
| 0
| 100
| bgcolor="#ff00ff" |
|-
| 9
| Green
| 0
| 50
| 0
| bgcolor="#008000" |
|-
| 10
| Cyan
| 0
| 50
| 50
| bgcolor="#008080" |
|-
| 11
| Sky Blue
| 0
| 50
| 100
| bgcolor="#0080ff" |
|-
| 12
| Yellow
| 50
| 50
| 0
| bgcolor="#808000" |
|-
| 13
| White
| 50
| 50
| 50
| bgcolor="#808080" |
|-
| 14
| Pastel Blue
| 50
| 50
| 100
| bgcolor="#8080ff" |
|-
| 15
| Orange
| 100
| 50
| 0
| bgcolor="#ff8000" |
|-
| 16
| Pink
| 100
| 50
| 50
| bgcolor="#ff8080" |
|-
| 17
| Pastel Magenta
| 100
| 50
| 100
| bgcolor="#ff80ff" |
|-
| 18
| Bright Green
| 0
| 100
| 0
| bgcolor="#00ff00" |
|-
| 19
| Sea Green
| 0
| 100
| 50
| bgcolor="#00ff80" |
|-
| 20
| Bright Cyan
| 0
| 100
| 100
| bgcolor="#00ffff" |
|-
| 21
| Lime
| 50
| 100
| 0
| bgcolor="#80ff00" |
|-
| 22
| Pastel Green
| 50
| 100
| 50
| bgcolor="#80ff80" |
|-
| 23
| Pastel Cyan
| 50
| 100
| 100
| bgcolor="#80ffff" |
|-
| 24
| Bright Yellow
| 100
| 100
| 0
| bgcolor="#ffff00" |
|-
| 25
| Pastel Yellow
| 100
| 100
| 50
| bgcolor="#ffff80" |
|-
| 26
| Bright White
| 100
| 100
| 100
| bgcolor="#ffffff" |
|}

===== To calculate the colour value =====

'''Red'''

0% => do not add anything

50% => add 3

100% => add 6

'''Green'''

0% => do not add anything

50% => add 9

100% => add 18

'''Blue'''

0% => do not add anything

50% => add 1

100% => add 2

Green Screen Colours

On a green screen (where all colours are shades of green), the colours (in the software/firmware colours), are in order of increasing intensity. So that black is very dark, and white is bright green, and colour 13 is a medium green. (Thanks to [[Mark Rison|Mark Rison]] for this information)

[[Category:Hardware]]

Gate Array

2009-02-20T20:22:08Z

Apollo: Fixed error in "Select Pen" table: bit 4 needs to be zero

Gate Array

== Introduction ==

The gate array is a specially designed chip exclusively for use in the Amstrad CPC and was designed by Amstrad plc.

In the CPC+ system, the functions of the Gate-Array are integrated into a single [[ASIC|ASIC]]. When the ASIC is "locked", the extra features are not available and the ASIC operates the same as the Gate-Array in the CPC allowing programs written for the CPC to work on the Plus without modification. The ASIC must be "un-locked" to access the new features.

In the [[KC Compact Computer|KC compact]] system, the functions of the Gate-Array are "emulated" in [[TTL logic|TTL logic]] and by the [[Zilog Z8536 CIO|Zilog Z8536 CIO]].

In the "cost-down" version of the CPC6128, the functions of the Gate-Array are integrated into a ASIC.

The Gate Array is described here, as it is in a standard CPC.

''What does it do?''

The Gate Array is responsible for the display (colour palette, resolution, horizontal and vertical sync), interrupt generation and memory arrangement.

== Controlling the Gate Array ==

The gate array is controlled by I/O. The gate array is selected when bit 15 of the I/O port address is set to "0" and bit 14 of the I/O port address is set to "1". The values of the other bits are ignored. However, to avoid conflict with other devices in the system, these bits should be set to "1".

The recommended I/O port address is &7Fxx.

The function to be performed is selected by writing data to the Gate-Array, bit 7 and 6 of the data define the function selected (see table below). It is not possible to read from the Gate-Array.

{|
|-
| ''Bit 7''
| ''Bit 6''
| ''Function''
|-
| 0
| 0
| Select pen
|-
| 0
| 1
| Select colour for selected pen
|-
| 1
| 0
| Select screen mode, rom configuration and interrupt control
|-
| 1
| 1
| Ram Memory Management (note 1)
|}

===== Note =====

This function is not available in the Gate-Array, but is performed by a device at the same I/O port address location. In the CPC464,CPC664 and KC compact, this function is performed in a memory-expansion (e.g. Dk'Tronics 64K Ram Expansion), if this expansion is not present then the function is not available. In the CPC6128, this function is performed by a PAL located on the main PCB, or a memory-expansion. In the 464+ and 6128+ this function is performed by the ASIC or a memory expansion. Please read the document on Ram Management for more information.

==== Pen selection ====

When bit 7 and bit 6 are set to "0", the remaining bits determine which pen is to have its colour changed. When bit 4 is set to "0", bits 3 to 0 define which pen is to be selected. When bit 4 is set to "1", the value contained in bits 3-0 is ignored and the border is selected.

The pen remains selected until another is chosen.

Each mode has a fixed number of pens. Mode 0 has 16 pens, mode 1 has 4 pens and mode 2 has 2 pens.

===== Summary =====

{|
|-
| ''Bit''
| ''Value''
| ''Function''
|-
| 7
| 0
| rowspan="2" | Gate Array function "Pen Selection"
|-
| 6
| 0
|-
| 5
| -
| not used
|-
| 4
| 1
| Select border
|-
| 3
| x
| rowspan="4" | Ignored
|-
| 2
| x
|-
| 1
| x
|-
| 0
| x
|}

 

{|
|-
| ''Bit''
| ''Value''
| ''Function''
|-
| 7
| 0
| rowspan="2" | Gate Array function "Pen Selection"
|-
| 6
| 0
|-
| 5
| -
| not used
|-
| 4
| 0
| Select pen
|-
| 3
| x
| rowspan="4" | Pen number
|-
| 2
| x
|-
| 1
| x
|-
| 0
| x
|}

==== Colour selection ====

Once the pen has been selected the colour can then be changed. Bits 4 to 0 specify the hardware colour number from the hardware colour palette.

Even though there is provision for 32 colours, only 27 are possible. The remaining colours are duplicates of those already in the colour palette.

===== Summary =====

{|
|-
| ''Bit''
| ''Value''
| ''Function''
|-
| 7
| 0
| rowspan="2" | Gate Array function "Colour selection"
|-
| 6
| 1
|-
| 5
| -
| not used
|-
| 4
| x
| rowspan="5" | Colour number x
|-
| 3
| x
|-
| 2
| x
|-
| 1
| x
|-
| 0
| x
|}

==== Hardware colour palette ====

{|
|-
| ''Colour Number''
| ''Colour Name''
| ''Color''
|-
| 0
| White
| bgcolor="#808080" |
|-
| 1
| White (note 1)
| bgcolor="#808080" |
|-
| 2
| Sea Green
| bgcolor="#00ff80" |
|-
| 3
| Pastel Yellow
| bgcolor="#ffff50" |
|-
| 4
| Blue
| bgcolor="#000080" |
|-
| 5
| Purple
| bgcolor="#ff0080" |
|-
| 6
| Cyan
| bgcolor="#008080" |
|-
| 7
| Pink
| bgcolor="#ff8080" |
|-
| 8
| Purple (note 1)
| bgcolor="#ff0080" |
|-
| 9
| Pastel Yellow (note 1)
| bgcolor="#ffff50" |
|-
| 10
| Bright Yellow
| bgcolor="#ffff80" |
|-
| 11
| Bright White
| bgcolor="#ffffff" |
|-
| 12
| Bright Red
| bgcolor="#ff0000" |
|-
| 13
| Bright Magenta
| bgcolor="#ff00ff" |
|-
| 14
| Orange
| bgcolor="#ff8000" |
|-
| 15
| Pastel Magenta
| bgcolor="#ff80ff" |
|-
| 16
| Blue (note 1)
| bgcolor="#000080" |
|-
| 17
| Sea Green (note 1)
| bgcolor="#00ff80" |
|-
| 18
| Bright Green
| bgcolor="#00ff00" |
|-
| 19
| Bright Cyan
| bgcolor="#00ffff" |
|-
| 20
| Black
| bgcolor="#000000" |
|-
| 21
| Bright Blue
| bgcolor="#0000ff" |
|-
| 22
| Green
| bgcolor="#008000" |
|-
| 23
| Sky Blue
| bgcolor="#0080ff" |
|-
| 24
| Magenta
| bgcolor="#800080" |
|-
| 25
| Pastel Green
| bgcolor="#80ff80" |
|-
| 26
| Lime
| bgcolor="#80ff00" |
|-
| 27
| Pastel Cyan
| bgcolor="#80ffff" |
|-
| 28
| Red
| bgcolor="#800000" |
|-
| 29
| Mauve
| bgcolor="#8000ff" |
|-
| 30
| Yellow
| bgcolor="#808000" |
|-
| 31
| Pastel Blue
| bgcolor="#8080ff" |
|}

===== Notes =====

This is not an official colour

Select screen mode and rom configuration

This is a general purpose register responsible for the screen mode and the rom configuration.

==== Screen mode selection ====

The function of bits 1 and 0 is to define the screen mode. The settings for bits 1 and 0 and the corresponding screen mode are given in the table below.

{|
|-
| ''Bit 1''
| ''Bit 0''
| ''Screen mode''
|-
| 0
| 0
| Mode 0, 160x200 resolution, 16 colours
|-
| 0
| 1
| Mode 1, 320x200 resolution, 4 colours
|-
| 1
| 0
| Mode 2, 640x200 resolution, 2 colours
|-
| 1
| 1
| Mode 3, 160x200 resolution, 4 colours (note 1)
|}

This mode is not official. From the combinations possible, we can see that 4 modes can be defined, although the Amstrad only has 3. Mode 3 is similar to mode 0, because it has the same resolution, but it is limited to only 4 colours.

Mode changing is synchronised with HSYNC. If the mode is changed, it will take effect from the next HSYNC.

==== Rom configuration selection ====

Bit 2 is used to enable or disable the lower rom area. The lower rom area occupies memory addressess &0000-&3fff and is used to access the operating system rom. When the lower rom area is is enabled, reading from &0000-&3FFF will return data in the rom. When a value is written to &0000-&3FFF, it will be written to the ram underneath the rom. When it is disabled, data read from &0000-&3FFF will return the data in the ram.

Similarly, bit 3 controls enabling or disabling of the upper rom area. The upper rom area occupies memory addressess &C000-&FFFF and is BASIC or any expansion roms which may be plugged into a rom board/box. See the document on upper rom selection for more details. When the upper rom area enabled, reading from &c000-&ffff, will return data in the rom. When data is written to &c000-&FFFF, it will be written to the ram at the same address as the rom. When the upper rom area is disabled, and data is read from &c000-&ffff the data returned will be the data in the ram.

Bit 4 controls the interrupt generation. It can be used to delay interrupts. See the document on interrupt generation for more information.

===== Summary =====

{|
|-
| ''Bit''
| ''Value''
| ''Function''
|-
| 7
| 0
| rowspan="2" | Gate Array function
|-
| 6
| 1
|-
| 5
| -
| not used
|-
| 4
| x
| Interrupt generation control
|-
| 3
| x
|
*1 Upper rom area disable
*0 Upper rom area enable

|-
| 2
| x
|
*1 Lower rom area disable
*0 Lower rom area enable

|-
| 1
| x
| rowspan="2" | Mode slection
|-
| 0
| x
|}

== Programming the Gate Array - Examples ==

Defining the colours, Setting pen 0 to Bright White.
<pre>LD BC,7F00 ;Gate Array port
LD A,%00000000+0 ;Pen number (and Gate Array function)
OUT (C),A ;Send pen number
LD A,%01000000+11 ;Pen colour (and Gate Array function)
OUT (C),A ;Send it
RET

Setting the mode and rom configuration,
Mode 2, upper and lower rom disabled.

LD BC,7F00 ;Gate array port
LD A,%10000000+%00001110 ;Mode and rom selection (and Gate Array function)
OUT (C),A ;Send it
RET
</pre>
==== Conversion chart ====

The hardware colour number is different to the colour range used by the firmware, so a conversion chart is provided for the corresponding firmware/hardware colour values and the corresponding colour name.

===== Note =====

The firmware keeps track of the colours it is using. Every VSYNC (assuming interrupts are enabled) the firmware sets the colours. This enables the user to have flashing colours. If the user selects a new colour using the gate array, the new colour will flash temporarily and then return to it's original colour. This is due to the firmware re- setting the colour. When using the firmware, use it's routines to select the colour, and the colour will remain.

{|
|-
| ''Firmware Colour Number''
| ''Colour Name''
| ''Hardware Number''
| ''Quick reference colour value''
| ''Color''
|-
| 0
| Black
| 20
| &54
| bgcolor="#000000" |
|-
| 1
| Blue
| 4
| &44
| bgcolor="#000080" |
|-
| 2
| Bright Blue
| 21
| &55
| bgcolor="#0000ff" |
|-
| 3
| Red
| 28
| &5C
| bgcolor="#800000" |
|-
| 4
| Magenta
| 24
| &58
| bgcolor="#800080" |
|-
| 5
| Mauve
| 29
| &5D
| bgcolor="#8000ff" |
|-
| 6
| Bright Red
| 12
| &4C
| bgcolor="#ff0000" |
|-
| 7
| Purple
| 5
| &45
| bgcolor="#ff0080" |
|-
| 8
| Bright Magenta
| 13
| &4D
| bgcolor="#ff00ff" |
|-
| 9
| Green
| 22
| &56
| bgcolor="#008000" |
|-
| 10
| Cyan
| 6
| &46
| bgcolor="#008080" |
|-
| 11
| Sky Blue
| 23
| &57
| bgcolor="#0080ff" |
|-
| 12
| Yellow
| 30
| &5E
| bgcolor="#808000" |
|-
| 13
| White
| 0
| &40
| bgcolor="#808080" |
|-
| 14
| Pastel Blue
| 31
| &5F
| bgcolor="#8080ff" |
|-
| 15
| Orange
| 14
| &4E
| bgcolor="#ff8000" |
|-
| 16
| Pink
| 7
| &47
| bgcolor="#ff8080" |
|-
| 17
| Pastel Magenta
| 15
| &4F
| bgcolor="#ff80ff" |
|-
| 18
| Bright Green
| 18
| &52
| bgcolor="#00ff00" |
|-
| 19
| Sea Green
| 2
|
|-
| 20
| Bright Cyan
| 19
| &53
| bgcolor="#00ffff" |
|-
| 21
| Lime
| 26
| &5A
| bgcolor="#80ff00" |
|-
| 22
| Pastel Green
| 25
| &59
| bgcolor="#80ff80" |
|-
| 23
| Pastel Cyan
| 27
| &5B
| bgcolor="#80ffff" |
|-
| 24
| Bright Yellow
| 10
| &4A
| bgcolor="#ffff80" |
|-
| 25
| Pastel Yellow
| 3
| &43
| bgcolor="#ffff80" |
|-
| 26
| Bright White
| 11
| &4B
| bgcolor="#ffffff" |
|}

This chart also gives a quick reference guide for programming the colours. The number is the colour number which can be sent directly, once the pen has been selected, to get the colour wanted.

Example:
<pre>ld bc,7f00+1 ;Gate array function (set pen)
;and pen number
out (c),c
ld bc,7f00 ;41
;Gate array function (set colour)
;and colour number
out (c),c
ret
</pre>
==== Pallette R,G,B definitions ====

There are 27 colours which are generated from red, green and blue mixed in different quantities. There are 3 levels of red, 3 levels of green and 3 levels of blue, and these can be thought of as off/no colour, half-on/half-colour, and on/full-colour.

To display a CPC image you will need to use a analogue monitor with a composite sync.

This table shows the relationship between hardware colour number, colour name and RGB mixing.

 

{|
|-
| ''Hardware Colour Index''
| ''Colour Name''
| ''R %''
| ''G %''
| ''B %''
| ''Color''
|-
| 0
| White
| align="right" | 50
| align="right" | 50
| align="right" | 50
| bgcolor="#808080" |
|-
| 1
| White
| align="right" | 50
| align="right" | 50
| align="right" | 50
| bgcolor="#808080" |
|-
| 2
| Sea Green
| align="right" | 0
| align="right" | 100
| align="right" | 50
| bgcolor="#00ff80" |
|-
| 3
| Pastel Yellow
| align="right" | 100
| align="right" | 100
| align="right" | 50
| bgcolor="#ffff80" |
|-
| 4
| Blue
| align="right" | 0
| align="right" | 0
| align="right" | 50
| bgcolor="#000080" |
|-
| 5
| Purple
| align="right" | 100
| align="right" | 0
| align="right" | 50
| bgcolor="#ff0080" |
|-
| 6
| Cyan
| align="right" | 0
| align="right" | 50
| align="right" | 50
| bgcolor="#008080" |
|-
| 7
| Pink
| align="right" | 100
| align="right" | 50
| align="right" | 50
| bgcolor="#ff8080" |
|-
| 8
| Purple
| align="right" | 100
| align="right" | 0
| align="right" | 50
| bgcolor="#ff0080" |
|-
| 9
| Pastel Yellow
| align="right" | 100
| align="right" | 100
| align="right" | 50
| bgcolor="#ffff80" |
|-
| 10
| Bright Yellow
| align="right" | 100
| align="right" | 100
| align="right" | 0
| bgcolor="#ffff00" |
|-
| 11
| Bright White
| align="right" | 100
| align="right" | 100
| align="right" | 100
| bgcolor="#ffffff" |
|-
| 12
| Bright Red
| align="right" | 100
| align="right" | 0
| align="right" | 0
| bgcolor="#ff0000" |
|-
| 13
| Bright Magenta
| align="right" | 100
| align="right" | 0
| align="right" | 100
| bgcolor="#ff00ff" |
|-
| 14
| Orange
| align="right" | 100
| align="right" | 50
| align="right" | 0
| bgcolor="#ff8000" |
|-
| 15
| Pastel Magenta
| align="right" | 100
| align="right" | 50
| align="right" | 100
| bgcolor="#ff80ff" |
|-
| 16
| Blue
| align="right" | 0
| align="right" | 0
| align="right" | 50
| bgcolor="#000080" |
|-
| 17
| Sea Green
| align="right" | 0
| align="right" | 100
| align="right" | 50
| bgcolor="#00ff80" |
|-
| 18
| Bright Green
| align="right" | 0
| align="right" | 100
| align="right" | 0
| bgcolor="#00ff00" |
|-
| 19
| Bright Cyan
| align="right" | 0
| align="right" | 100
| align="right" | 100
| bgcolor="#00ffff" |
|-
| 20
| Black
| align="right" | 0
| align="right" | 0
| align="right" | 0
| bgcolor="#000000" |
|-
| 21
| Bright Blue
| align="right" | 0
| align="right" | 0
| align="right" | 100
| bgcolor="#0000ff" |
|-
| 22
| Green
| align="right" | 0
| align="right" | 50
| align="right" | 0
| bgcolor="#008000" |
|-
| 23
| Sky Blue
| align="right" | 0
| align="right" | 50
| align="right" | 100
| bgcolor="#0080ff" |
|-
| 24
| Magenta
| align="right" | 50
| align="right" | 0
| align="right" | 50
| bgcolor="#800080" |
|-
| 25
| Pastel Green
| align="right" | 50
| align="right" | 100
| align="right" | 50
| bgcolor="#80ff80" |
|-
| 26
| Lime
| align="right" | 50
| align="right" | 100
| align="right" | 0
| bgcolor="#80ff00" |
|-
| 27
| Pastel Cyan
| align="right" | 50
| align="right" | 100
| align="right" | 100
| bgcolor="#80ffff" |
|-
| 28
| Red
| align="right" | 50
| align="right" | 0
| align="right" | 0
| bgcolor="#800000" |
|-
| 29
| Mauve
| align="right" | 50
| align="right" | 0
| align="right" | 100
| bgcolor="#8000ff" |
|-
| 30
| Yellow
| align="right" | 50
| align="right" | 50
| align="right" | 0
| bgcolor="#808000" |
|-
| 31
| Pastel Blue
| align="right" | 50
| align="right" | 50
| align="right" | 100
| bgcolor="#8080ff" |
|}

==== RGB assignments for the software colours ====

This is simply a sidenote to illustrate a pattern in the RGB assignments of the software colours and to show how their value is calculated.

{|
|-
| ''Firmware Colour Number''
| ''Colour Name''
| ''R %''
| ''G %''
| ''B %''
| ''Color''
|-
| 0
| Black
| 0
| 0
| 0
| bgcolor="#000000" |
|-
| 1
| Blue
| 0
| 0
| 50
| bgcolor="#000080" |
|-
| 2
| Bright Blue
| 0
| 0
| 100
| bgcolor="#0000ff" |
|-
| 3
| Red
| 50
| 0
| 0
| bgcolor="#800000" |
|-
| 4
| Magenta
| 50
| 0
| 50
| bgcolor="#800080" |
|-
| 5
| Mauve
| 50
| 0
| 100
| bgcolor="#8000ff" |
|-
| 6
| Bright Red
| 100
| 0
| 0
| bgcolor="#ff0000" |
|-
| 7
| Purple
| 100
| 0
| 50
| bgcolor="#ff0080" |
|-
| 8
| Bright Magenta
| 100
| 0
| 100
| bgcolor="#ff00ff" |
|-
| 9
| Green
| 0
| 50
| 0
| bgcolor="#008000" |
|-
| 10
| Cyan
| 0
| 50
| 50
| bgcolor="#008080" |
|-
| 11
| Sky Blue
| 0
| 50
| 100
| bgcolor="#0080ff" |
|-
| 12
| Yellow
| 50
| 50
| 0
| bgcolor="#808000" |
|-
| 13
| White
| 50
| 50
| 50
| bgcolor="#808080" |
|-
| 14
| Pastel Blue
| 50
| 50
| 100
| bgcolor="#8080ff" |
|-
| 15
| Orange
| 100
| 50
| 0
| bgcolor="#ff8000" |
|-
| 16
| Pink
| 100
| 50
| 50
| bgcolor="#ff8080" |
|-
| 17
| Pastel Magenta
| 100
| 50
| 100
| bgcolor="#ff80ff" |
|-
| 18
| Bright Green
| 0
| 100
| 0
| bgcolor="#00ff00" |
|-
| 19
| Sea Green
| 0
| 100
| 50
| bgcolor="#00ff80" |
|-
| 20
| Bright Cyan
| 0
| 100
| 100
| bgcolor="#00ffff" |
|-
| 21
| Lime
| 50
| 100
| 0
| bgcolor="#80ff00" |
|-
| 22
| Pastel Green
| 50
| 100
| 50
| bgcolor="#80ff80" |
|-
| 23
| Pastel Cyan
| 50
| 100
| 100
| bgcolor="#80ffff" |
|-
| 24
| Bright Yellow
| 100
| 100
| 0
| bgcolor="#ffff00" |
|-
| 25
| Pastel Yellow
| 100
| 100
| 50
| bgcolor="#ffff80" |
|-
| 26
| Bright White
| 100
| 100
| 100
| bgcolor="#ffffff" |
|}

===== To calculate the colour value =====

'''Red'''

0% => do not add anything

50% => add 3

100% => add 6

'''Green'''

0% => do not add anything

50% => add 9

100% => add 18

'''Blue'''

0% => do not add anything

50% => add 1

100% => add 2

Green Screen Colours

On a green screen (where all colours are shades of green), the colours (in the software/firmware colours), are in order of increasing intensity. So that black is very dark, and white is bright green, and colour 13 is a medium green. (Thanks to [[Mark Rison|Mark Rison]] for this information)

[[Category:Hardware]]