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Internal 512 KB [[Category:DIY]] [[Category:Memory expansions]]A project to upgrade a CPC6128 to 512K RAM expansion for (total), done by replacing the CPC6128 from 's RAM chips, and its PAL banking chip, the project was released 1987 in german magazine '''c't, issue 10/1987Magazin'''. The DIY project name is '''CPC 6512'''. The mod requires to remove (or disable) the sixteen RAM chips on the CPC6128 mainboard, and to replace them by bigger chips, plus whatever additional bank selection logic.

The memory is accessed via Port 7Fxxh, as on [[Standard Memory Expansions]]* '''PAL Replacement''' - Replace the old PAL (IC118) by the new daughterboard. Since Most signals connect to the internal RAM is removed, its total capacity is only 512K PAL socket (unlike standard 512K expansions which provide 64K internal plus 512K external memorygreen in schematic), ie. 576K totala extra few wires connect elsewhere on mainboard (red). Altogether, as an optional "bonus" feature, the c't expansion works like circuit contains logic for a 448K dk'tronics expansion 3rd floppy drive (leaving the banks selected via OUT [7Fxxh],FCh..FFh unusedblue).

One half (256K) of the total (512K) expansion memory can be accessed as Video RAM (with normal expansions, only 64 KB are accessible as VRAM)<gallery>File:CPC6512 ct magazin schematic. This is making the expansion slightly incompatible with the dk'tronics standard. However, usually expansion memory is mapped to 4000h-7FFFh, whilst VRAM is usually mapped to C000h-FFFFh. So, most existing software may work with it, without accidently displaying garbage on the screenpng|SchematicFile:CPC6512 ct magazin pcb.jpg|PCB</gallery>

== Compatibility Problems == * Unknown which RAMDIS is not supported, not a problem in most cases, but won't work with some special types of expansion hardware, like [[Multiface II]].* The expansion seems to have been designed independently of [[Standard Memory Expansions]] like the dk'tronics one. So, there is no (intended) compatibility. However, both c't and dk'tronics are designed around the CPC6128 banking mechanism, so they do work similar in some ways. Namely, both can map expansion banks to 4000h..7FFFh, but there are usable as VRAMseveral differences:** The first four 16K For the mapping to 4000h..7FFFh, dk'tronics uses values CCh..CFh, D4h..C7h, DCh..DFh, ... FCh..FFh whilst c't uses values C8h..DFh. Some of these values do overlap, resulting in some (unintended) semi-compatibility, but there's still one big difference: along with the above values, dk'tronics maps bank 3 to C000h..FFFFh, whilst c't maps bank 7 to that region. == Memory Configurations == The memory is controlled by OUT [7Fxxh],C0h..DFh instructions. Values C0h..C7h are working same as on normal CPC6128s. Values C8h..DFh do access the additional RAM banks (probablyC8h..D3h when using the cut-down 320K upgrade variant) usuable as VRAM .  OUT [7Fxxh],C0h+... 0 1 2 3 4 5 6 7 8..31 ------------------------------------------------------- Bank at C000h..FFFFh 3 7 7 7 3 3 3 3 7 (as !) Bank at 8000h..BFFFh 2 2 6 2 2 2 2 2 2 Bank at 4000h..7FFFh 1 1 5 3 4 5 6 7 8..31 Bank at 0000h..3FFFh 0 0 4 0 0 0 0 0 0 == PAL Source Code == Below is a typed-up and commented copy of the PALASM source code from the original article.  D7D6 D0 D3 D4 D1 D2 NCAS A15 A14 GND ;pin 1..10 CPU A15S AMUX MUX LCLK CAS1 CAS0 IOWR A14S VCC ;pin 11..20 IF (VCC) /LCLK= D7D6 * /A15 * /IOWR ;load external latch on all 64K CPC modelsOUT [7Fxxh],C0h..FFh IF (VCC) /CAS0= /NCAS * /D4 + ;bank bit4=0, select bank 0..15 (CPU and CRTC) /CAS0= /NCAS * A15 + /CAS0= /NCAS * The next four 16K /A14 + /CAS0= /NCAS * CPU IF (VCC) /CAS1= /NCAS * D4 * /A15 * A14 * /CPU ;bank are bit4=1, select bank 16..31 (hopefullyCPU at 4000h..7FFFh only) not usuable as VRAM IF (for CPVCC) /MA14S= /A14 + compatibility, which uses them as Work RAM ;bank bit0 /D0 * D2 * /A15 + /D0 * D3 * /A15 + /D0 * D4 * /A15 IF (VCC)/A15S= /A14 * /A15 + ;bank bit1 /D1 * /A15 + /D4 * /D3 * /D2 * /D0 * /A15 + /D4 * /D3 * /D2 * /D1 * /A15 IF (VCC) /AMUX= /D0 * D1 * /D2 * /D3 * /D4 * /CPU * /MUX + A15 * A14 * /D2 * D0 * /CPU * /MUX + A15 * A14 * /D2 * D1 * /CPU * /MUX + A15 * A14 * D3 * /CPU * /MUX + A15 * A14 * D4 * /CPU * /MUX + /A15 * A14 * D2 * /CPU * /MUX + ;bank bit2 /A15 * A14 * D3 * /CPU * MUX ;bank bit3 IF (GND) /MUX = /MUX ;dummy (do not output anything on this pin) IF (GND) /IOWR=/IOWR ;dummy (do not output anything on this pin) '''Note:''' For further banks itVRAM access, bank bits 2,3,4 are forced to zero (by above formulas), bank bit 0,1 are coming from the CRTC, passed directly to IC109 (without going through the PAL), so, the RAM banking affects only the CPU's totally unknown if they are used as VRAM or memory accesses, not* Unknown if itthe CRTC's fully dk'tronics compatiblevideo memory accesses. Some notes on the syntax:* The first two lines assign the pin-outs. Observe that leading "/" slashes are omitted here. For example, "/CPU" (in schematic) becomes "CPU" (in source code). Accordingly "/CPU" (in source code) would be double-negated "//CPU" aka "CPU" (in schematic).* The "IF (condition) signal=" part means that "signal" becomes an output when condition is true. In the above source code, condition is always true (VCC), or more like incompletely implemented Inicron variant, for the last 2 lines, always false (GND).* Unknown what happens on accessing The "*" and "+" operators are meaning "* = AND", "+ = OR". The idea behind that confusing syntax was to make it "easier" to learn for people who are trained only in basic maths (the unused region via OUT [7Fxxh]formulas do also work when treating *=multiply,FChand +=plus.For example: 1+0+1+1 = 3 = nonzero = true).FFh* Chipset / Schematic is unknownThere must be some priority ordering in the formulas: Either * before +, or operations inside of a line before merging the results of the separate lines (in above examples, both ordering methods do work).

<gallery>Image* [[Media:NoPictureCPC6512 ct magazin part 1.gif|pdf]] - c't, issue 10/1987 (- RAM schematic)Expansion SchematicImage* [[Media:NoPictureCPC6512 ct magazin part 2.gif|pdf]] - c't, issue 11/1987 (- RAM disc Disc driver)<for CP/gallery>M Plus

The '''CPC 6512''' c't ''Memory Expansion'' is not to be confused with issues '''CPC 6512''' and '''CPC 6513''' of the more popular ''World War II Fanzine'' from Concord Publications Company.== Related hardware modifications ==<gallery>File:Cpc6512.jpg* [[CPC_6320_/_CPC_6512_-_internal_320K_/_512K_for_CPC_6128|CPC 6320 / CPC 6512(by eto) - similar logic, but fully standards compatible]]File* [https:Cpc6513//cpcwiki.jpg|CPC 6513eu/forum/index.php/topic,662.msg7113.html#msg7113 Bank Swapper by Khany/Cherry-T] (less complex: bank-exchanging toggle, no memory expansion; 1993)<* [[CPC4MB| CPC4MB memory upgrade by Yarek]] (more advanced; 2005/gallery>2006)