Changes
The '''standard''' memory expansions are often credited to [[Dk'tronics ]] and [[Dobbertin ]] (not sure which company initially developed it though). There's also an '''extended standard''' which may be credited to Yarek or probably [[RAM7 ]] (not sure who came first hereseen at least in comp.sys.amstrad.8bit FAQ v0.90, too11 september 1997)or [[Yarek]].
== Technical ==
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.
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=== Standard 128K-512K Expansions (dk'tronics/dobbertin-style) ===
Expansions bigger than 64K combine the CPC6128-style mapping with some formerly unused chips bits in the fourth Gate Array registervalue written to the RAM select:
5-3 Bank number in 64K units (for expansions bigger than 64K) (max = 512K)
2-.0 Bank mapping in 16K fragments (RAM configuration as on normal CPC 6128 Gate Array)The 16K fragments are consisting of 8 banks. Banks 0-3 are the internal RAM, banks 4-7 are external RAM (CPC6128 taken from the currently selected 64K block).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).
aaa = upper bits of 64K bank selection (512K-step) (A8,A9,A10 bits)
bbb = lower bits of 64K bank selection (64K-step) (D3,D4,D5 bits)
ccc = mapping of 16K fragments configuration (as in CPC6128) (D0,D1,D2 bits)
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 commandregister at FB7Fh is mirrored to these locations. Using 7B80h..7BFFh wouldfix that problem, but might conflict with other connected expansionhardware.
* '''Compatibility''' - The first 512K (Port 7Fxxh) are fully compatible with dk'tronics. Using the next 1.5MB (Port 7Exxh,7Dxxh,7Cxxh) should work without conflicting with the other hardware expansions.
* [[Dk'tronics memory expansion|Dk'tronics Memory Expansion and Silicon Disc]] - 64K and 256K expansions
* [[Dobbertin Memory Expansion]]
* [[RAM BOX]] 512Kb memory expansion '''(is that lowercase "b" meaning 512kbit=64Kbyte ???)'''
* [[SYMBiFACE II]] - includes (among others) 512K RAM expansion
* [[X-MEM]]
* [[Old_School_512K_RAM_Expansion]]
* [[CPC_6320_-_internal_320K_for_CPC_6128|CPC 6320 - internal 320K for CPC 6128]]
== Extended-Standard Expansions ==
* [[CPC4MBGemini]] (DIYShinra - PulkoTronics) - compatible with standard 512 Kbyte expansion (plus extra extended-standard 3.5 MBbyte512 Kbyte), also handles special case for Amstrad Plus ASIC* [[RAM7 2MB memory expansion]] ([[RAM7]]) - compatible with standard 512 Kbyte expansion (plus extra extended-standard 1.5 MBbyte)* [[CPC4MB]] ([[Yarek]]) (DIY) - compatible with standard 512 Kbyte expansion (plus extra extended-standard 3.5 MBbyte)
== Semi-Standard Expansions ==
* [[Aleste 520EX]] - a CPC clone that allows to access 256K (of its total 512K memory) in semiInicron-standard style fashion (ie. as on a 64K computer with 192K expansionwhich can be mapped to 4000h..7FFFh).* [[Inicron RAM-Box]] - not fully compatible with standard expansions (semi-standard)These two "semi-standard" ones can map some expansion banks RAM only to 4000h..7FFFh).
== Non-Standard Expansions ==
* [[c't 512 KB internal RAM expansion]] - works similar to dk'tronics expansions, but, alltogether, there isn't much compatibility between c't and dk'tronics.
* [[Otten & Fecht 1 MB RAM-Disc]] - Accessed through I/O ports (RAM is not mapped to memory)
* [[Vortex Expansions RAM card]] - an older expansion, uses 32K-banks, not compatible with the later standard
== Expansions that are unknown how they work, and if they are standard or not ==
* [[Data Media SP64Memory Expansion]] - all unknownan older thing, said to be not dk'tronics compatible, nothing else known
* [[Phoenix M64]] - all unknown
[[Category:Hardware]][[Category:Memory expansions| ]][[Category:DATA Storage]][[Category:Expansion ROM]][[Category:Peripherals|*]]
