POR column indicates whether a register has power-on reset. A "N" indicates that the contents of a register are undefined at power-on.
Beware, when booting your software from cartridge. The Z80 is in Interrupt Mode 0 by default. The FDC is in DMA mode by default. And the hardware sprites memory has random value.
Anyway, you have to initialize all internal components (Z80, PPI, CRTC, AY, etc) when you are booting from cartridge.
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