Changes
Writing to Port DFxxh selects the Upper ROM Bank Number (in range of 00h..FFh) to be mapped to memory at C000h..FFFFh. Whether or not the ROM is enabled (or if RAM is mapped to that region) is controlled by the [[Gate Array]].
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== Technical ==
By default, if there are no peripherals issuing ROMDIS=HIGH, then BASIC is mapped to all ROM banks in range of 00h..FFh.
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== Common ROM Bank Numbers ==
FFh BASIC (or ROM with similar ID; for the crude 128K RAM-size detection in CP/M+)
FFh BASIC (or ROM with similar ID; for the BIOS key scan detection in AMSDOS+)
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== Other Bank Numbers ==
* You may want to add a list of devices with ROM here, please also include their fixed bank number(s), or selectable range of bank number(s))
* Not sure if there are devices with incompletely decoded bank numbers? Eg. a ROM mapped to bank 06h, but also mirrored to 16h, 26h, 36h, etc. If so, these addresses should be listed here, too.
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== ASIC ROM numbering system ==
On CPC, this port is really simple. It simply accepts a logical ROM number from 0-255.
On Plus, this port behaves in 2 modes, indicated by bit7:
* if bit7 = 0, it accepts a logical ROM number from 0-127
* If bit7 = 1, bits6..5 are ignored and bits4..0 is a physical ROM number from 0-31
On a barebone CPC, the logical ROMs available are:
*ROM 0: BASIC
*ROM 7: AMSDOS (except on CPC464)
On a Plus with factory cartridge, the physical ROMs available are:
*ROM 0: Firmware
*ROM 1: BASIC
*ROM 2: Unused
*ROM 3: AMSDOS
*ROM 4: Burnin' Rubber ROM 0
*ROM 5: Burnin' Rubber ROM 1
*ROM 6: Burnin' Rubber ROM 2
*ROM 7: Burnin' Rubber ROM 3
Physical ROM 1 is mapped to logical ROM 0 and physical ROM 3 is mapped to logical ROM 7.
Logical ROMs can be replaced by using a ROM box while physical ROMs cannot be replaced.
[[Category:Programming]][[Category:Memory expansions]][[Category:Peripherals]][[Category:CPC Internal Components]]
