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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 10/1987'''. The DIY project name is '''CPC 6512'Magazin''.

One half (256K) of the total (512K) expansion memory can be accessed as Video RAM (with normal expansions, only 64 KB are accessible as Video RAM). == The c't expansion is compatible with [[Standard Memory Expansions]], and provides the additional CRTC feature, but it misses 64 KB usually addressed via I/O ports &7FFC, &7FFD, &7FFE and &7FFF.Circuit ==

One issue later, c* 't 11/1987, ''DRAM Replacement''' - Replace the magazine published a driver which creates a RAM disk within the additional memorysixteen old 64Kx1 DRAM chips (IC119-IC134) by new 256Kx1 DRAMs. This RAM disk can be used in [[AMSDOS]]The chips have same pinouts, only pin 1 is changed (old: NC, new: A8 row:column address signal). Optionally, replace only bank 0 (IC127-IC134) for getting only 320K (256K+64K) instead of 512K total (2x256K).

I<gallery>File:CPC6512 ct magazin schematic.png|SchematicFile:CPC6512 ct magazin pcb.jpg|PCB</O Ports gallery> '''Component List''' 16x 41256 (256Kx1 DRAM) ;replacing the CPC6128's 16 built-in 64Kx1 DRAMs 1x PAL 16L8 ;replacing the CPC6128's built-in PAL 1x 74LS38 ;Quad 2-input NAND, OC 1x 74LS273 ;8bit latch, of which only 5bit are &7FC4used here 1x 2200 Ohm resistor ;pull-up for OC output 1x 470 Ohm resistor ;pull-up for OC output 1x 47 Ohm resistor ;purpose unknown (noise related? shortcut protection?) == Compatibility Problems == * RAMDIS is not supported, not a problem in most cases, but won't work with some special types of expansion hardware, &7FC5like [[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.&7FF7. &7FC0 selects However, both c't and dk'tronics are designed around the first 64 KBCPC6128 banking mechanism, so they do work similar in some ways. With this Namely, both can map expansion banks to 4000h..7FFFh, but there are several differences:** For the CPC can 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 512 KB the additional RAM totalbanks (C8h. With .D3h when using the cut-down 320K upgrade variant).  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 (!) 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 OUT [7Fxxh],C0h..FFh IF (VCC) /CAS0= /NCAS * /D4 + ;bank bit4=0, select bank 0..15 (CPU and CRTC) /CAS0= /NCAS * A15 + /CAS0= /NCAS * /A14 + /CAS0= /NCAS * CPU IF (VCC) /CAS1= /NCAS * D4 * /A15 * A14 * /CPU ;bank bit4=1, select bank 16..31 (CPU at 4000h..7FFFh only) IF (VCC) /A14S= /A14 + ;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 VRAM 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 memory accesses, not the CRTC's video memory accesses. Some notes on the syntax:* The first two lines assign the pin-outs. Observe that leading "normal/" 512 KB 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, for the last 2 lines, always false (GND).* The "*" and "+" operators are meaning "* = AND", "+ = OR". The idea behind that confusing syntax was to make it can access 576 KB "easier" to learn for people who are trained only in basic maths (64 KB the formulas do also work when treating *=multiply, and + 512 KB=plus. For example: 1+0+1+1 = 3 = nonzero = true).* There 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)