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Extra ROM banks for CPC

The CPC can use 256 ROM banks, that are mapped to #C000..#FFFF. Two of them are already installed: #00 is BASIC, #07 is AMSDOS (except CPC464). Banks 0 to 15 are initialized by the system (downto from 15) and can contin RSXes.

With external interface or internal upgrade more ROM banks can be added. Extra banks can be used for extra BASIC commands (RSX), new interface software (CPCISA, serial ports), operating system (e.g. FutureOS) and even as storage for programs or diskimages converted to CPC+ cartridges.


This external interface has 128kB SRAM with battery backup (8 banks seen as 0..7) and slot for EPROM configurable as bank 0..15. In case of conflict, banks 0..7 can be disabled separately. Also there are jumpers to select which 16kB part of 32kB or 64kB EPROM is used.

To reprogramm the RAM banks that work as ROM, the interface mode must be manually switched.

There's a upgrade for Inicron ROM-RAM-BOX. Second 128kB SRAM can be also mounted, what gives 256kB for ROM banks. It is even possible to mount four such chips, getting 512kB. The DIP-switch disables 2 or 4 bank at once (e.g. #02, #0A, #12, #1A).

Also, one 512kB SRAM chip can be mounted, but the /CS signal must be controlled differently to protect the contents while power-off.

Symbiface II

Also simulates ROM with battery backuped RAM. Its "ROM" feature is similar to Inicron ROM-RAM-BOX. There are also eight switches for 32 banks. But the banks are write-enabled in #4000..#7FFF area after IN from #FD17 port. OUT to this port switches back to ROM mode.


The two internal PROMs can be replaced with 29F040 Flash EEPROM. Small cricuit redirects the system ROM to bank 31. See links below.

AmsDOS note

It is recommended to put active DISK.ROM as bank 15 and also inactive as bank 7 (change first byte from #01 to #FE). So, the DISK.ROM is initialized first (as 15) and no other bank (8..14) can reserve space before usual AmsDOS workarea (#A700..#ABAF). The copy in bank 7 increases compatibility, when a program directly selects bank 7 for disk operations.

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Files for download

rrb4.png 47.4kB (2006-07-06 23:14)
Inicron ROM-RAM-BOX schematics (CPC slot omitted).
romcard.jpg 34.5kB (2004-11-25 02:04)
Board with 128kB SRAM with battery backup that works like 8 ROM banks.
manuelramcard.zip 90.5kB (2004-11-06 02:47)
[fr] User manual for Ramcard (32kB or 128kB SRAM with "ROM" banks) by RAM7.
amstrad_rom_expander.pdf 2244.0kB (2004-11-05 11:20)
[en] Scanned description of 6 × 16kB EPROM extension.
romrambox.zip 349.4kB (2004-11-05 11:16)
128kB SRAM and 16kB EPROM extenstion for CPC6128. [de] Description how to build. By Inicron, 1995.

Links to other pages

See also

Amstrad CPC 4MB ROM upgrade
Internal and external 4MB ROM (Flash EEPROM) upgrade for Amstrad CPC.
FutureOS / CPC
Operating system for Amstrad CPC.



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© 2009-12-28 21:50 Jarek Adamski, http://8bit.yarek.pl