Changes

The standard expansions are based on the RAM banking logic from the CPC6128, ie. equivalent This is handled by a PAL16L8 but to the programmer it appears to be the fourth register in the [[Gate Array]] register in . The I/O decoding is different to the CPC6128 (or more preciselyGate-Array.* PAL16L8 decodes A15=0 only* Gate-Array decodes A15=0 and A14=1 To access the RAM and Gate-Array port 7fxx is used. In addition the RAM answers when the data has bit 7=1 and bit 6=1, which is unused in the PAL that assists its Gate -Array chip). External expansions have their own PAL or hardware which performs the same operation. Later CPC revisions with the costdown ASIC and the Plus have the RAM expansion logic inside their ASICs. ---- === Simple 64K Expansion (CPC6128-style) ===

* For full CPC6128 compatibility one may need some patches (eg. CP/M Plus will stiff still refuse to work; because it "detects" the 128K by checking the BASIC ROMs version number)

Expansions bigger than 64K combine the CPC6128-style mapping with some formerly unused chips in the fourth Gate Array register:---

Gate Array, === Standard 128K-512K Expansions (dk'tronics/dobbertin-style) === Expansions bigger than 64K combine the CPC6128-style mapping with some formerly unused bits in the value written to the RAM select: Port 7Fxxh: 7-6 Must be 3 (aka Gate Array Register 3)both set to 1

2-.0 Bank mapping in 16K fragments (RAM configuration as on normal CPC 6128 Gate ArrayCPC6128 taken from the selected bank '''Caution''' - The 64K bank numbers don't always start at bank 0 (In the Dk'tronics 256K Silicon Disc, the 64K banks are numbered 4..7). ---- === Extended 1M-4M Expansions (RAM7/Yarek-style) === Expansions bigger than 512K extend that above standard. The 16K fragments LSBs of the 64K bank number is kept in D5-D3 data bits (as above), the MSBs of the 64K bank number are consisting in A10-A8 address bits. Typically in inverted form (so the first 512K block is accessed via Port 7Fxxh, the next via 7Exxh, etc.  OUT [01111aaaxxxxxxxx],11bbbccc aaa = upper bits of 8 banks64K bank selection (512K-step) (A8,A9,A10 bits) bbb = lower bits of 64K bank selection (64K-step) (D3,D4,D5 bits) ccc = configuration (as in CPC6128) xxxxxxxx = should be set so that it doesn't conflict with other ports (*) (*) For example 7B01h or 7B7Fh would be no good, because the FDC command register at FB7Fh is mirrored to these locations. Banks 0Using 7B80h..7BFFh would fix that problem, but might conflict with other connected expansion hardware. * '''Compatibility''' -3 The first 512K (Port 7Fxxh) are fully compatible with dk'tronics. Using the internal RAMnext 1.5MB (Port 7Exxh, banks 47Dxxh,7Cxxh) should work without conflicting with the other hardware expansions. * '''Compatibility Problems''' -7 The last 2MB (Port 7Bxxh,7Axxh,79xxh,78xxh) can conflict with other hardware. As workaround: Either leave them unused, or use values for "xx" that do not conflict with your hardware (which values are external RAM good for "xx" and which aren't good depends on what other hardware you have connected) (taken from the currently selected 64K blockand obviously, different "xx" may be needed in 7Bxxh as in 7Axxh, for example).

Standard expansions can contain between 64K and 512K memory. * A '''nnK expansion ''' adds '''nn Kbytes ''' to the internal '''64 Kbytes ''' in the CPC. So the resulting total size is '''nn+64 Kbytes'''.* This That '''nn+64 Kbytes''' formula does in most (or all ) cases also apply on the '''CPC 6128''': ** only 64 Kbytes of it's internal memory are used (** the 2nd half of internal memory is disabled and replaced by the expansion RAM** so, the resulting size is only nn+64Kbytes, not nn+128 Kbytes)

* [[Dk'tronics memory expansion|Dk'tronics Memory Expansion and Silicon Disc]] - 64K and 256K expansions

* [[CPC4MB]] (DIY) - compatible with standard 512 Kbyte expansion (plus extra non-standard 3.5 MBbyte)* [[RAM BOX]] 512Kb memory expansion '''(is that lowercase "b" meaning 512kbit=64Kbyte ???)'''* The first 192K (of total 512K) in [[Aleste 520EX]] are standard compatible

* [[Inicron c't 512 KB internal RAM-Boxexpansion]] - not fully compatible with standard works similar to dk'tronics expansions, but, alltogether, there isn't much compatibility between c't and dk'tronics.

* [[Vortex Expansions RAM card]] - nonan older expansion, uses 32K-banks, not compatible with the later standard

* [[RAM7 2Mb memory expansion]] - is that 2Mbit or 2Mbyte? what I/O ports would be used to access 2MByte?* [[Data Media SP64Memory Expansion]] - all unknown* [[Dkan older thing, said to be not dk'tronics Silicon Disc]] ([[Dk'tronics]]) - all unknowncompatible, nothing else known