Amstrad Whole Memory Guide - BASIC support - Revision history

Ygdrazil at 10:49, 25 August 2014

2014-08-25T10:49:56Z

CPCLER: /* Using the Maths Calls */

2008-07-16T09:21:26Z

‎Using the Maths Calls

CPCLER at 09:20, 16 July 2008

2008-07-16T09:20:34Z

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CPCLER at 07:44, 16 July 2008

2008-07-16T07:44:15Z

CPCLER: New page: Chapter 13 in the book Amstrad Whole Memory Guide. == Scanned pages == Image:AWMG page121.jpg|page 121 Image:AWMG page122.jpg|page 122 Image:AWMG page123.jpg|page 123 Image...

2008-07-02T06:58:02Z

New page: Chapter 13 in the book Amstrad Whole Memory Guide. == Scanned pages == <gallery> Image:AWMG page121.jpg|page 121 Image:AWMG page122.jpg|page 122 Image:AWMG page123.jpg|page 123 Image...

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		+	[[Category:CPC Firmware]]

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 Notable omission are routines for the input and output of numeric data, which is handled by the main interpreter. The input process can be complicated by the need to cover binary, decimal and hexadecimal bases, and by the fact that alphabetic data may also be involved. However, in broad terms the process involves;
 (a. Checking that the data is numeric.
 (b. Converting from ASCII to binary values.
 (c. Multiplying the number already input by the number base.
 (d. Adding the new digit.
 (e. Looping to A.
 Exit from the loop is usual dependent on a non-numeric being found at stage a.

← Older revision		Revision as of 07:44, 16 July 2008
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	Chapter 13 in the book [[Amstrad Whole Memory Guide]].		Chapter 13 in the book [[Amstrad Whole Memory Guide]].
		+
		+	== BASIC SUPPORT ==
		+
		+	The entries to the 2A98—37FF section of the lower ROM are not officially defined, because they are more a part of the BASIC interpreter than of the operating system. However, the 49 entries hold a host of treasures, especially for those whose programs involve mathematics.
		+
		+	The first entry, via BD3A, accesses the EDIT system, which is rather too specialised to be of general interest, being mainly concerned with the interpretation of various key combinations and the modification of data held in a buffer, the Start of which is defined in HL on entry.
		+
		+	The entries relating to floating point arithmetic are of much more general importance.
		+
		+	== Floating Point ==
		+
		+	A five—byte floating point system is used. For example:
		+
		+	86 65 2E EØ D3
		+
		+	The first byte is the exponent. Subtracting &80 gives 6, so the value of the exponent is 2t6 = 64. The remaining bytes form the mantissa, and the overall value of the number is found by multiplying together the values of the exponent and the mantissa.
		+	The most significant bit of the second byte is the sign bit. In this case it is Ø, so the number is positive. However, the true value of the bit in numeric terms is always 1, so the value of the last four bytes — the mantissa — is:
		+
		+	E62EEØD3 = 3,845,054,675
		+

	== Scanned pages ==		== Scanned pages ==