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Z80 BootROM Copy V0.1 [2018] |
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Production Info
Submitted by XmikeX on 30 October 2018
Why must Z80 be invoked to copy the Z80 BootROM ? ... This is because the Z80 BootROM is always invsible to 8502, as noted:
From Compute's Mapping the Commodore 128, page 334:
A bit of 128 hardware trivia: Since the MMU configuration register setting in bits 4-5 for character ROM is also the one which selects screen editor ROM at 49152-53247/$C000-$CFFF and Kernal ROM at 57344-65535/$E000-$FFFF, you might expect that character patterns are stored between the screen editor and Kernal routines in the 16K ROM chip designated U35. However, this is not the case. Character patterns are stored in a separate 4K ROM chip, designated U18.
So what's between 3248-57343/$D000-$DFFF in the ROM chip containing the screen editor and Kernal? That's where the ROM routines for CP/M mode are stored.
The memory-shuffling capabilities of the MMU and PLA allow this area of ROM to appear at addresses 0-4095/$0000-$0FFF when CP/M mode is selected. This section of ROM is always invisible to 128 mode. |
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