Changes

Upgrade of [[Category:DIY]] [[Category:Memory expansions]]A project to upgrade a CPC6128 to 512K RAM (total), done by replacing the CPC 6128CPC6128's internal RAM to 512 KiB as proposed in chips, and its PAL banking chip, the article '''Aus David wird Goliath: 512 KB RAM für Schneider CPC''' project was released 1987 in issue 10/1987, pages 156 to 162 of the German IT german magazine '''c'tMagazin'''. 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 standardpng|SchematicFile:CPC6512 ct magazin pcb. 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 screen. == Installation Guide ==jpg|PCB=== Components ===</gallery>

== Missing Info Memory Configurations ==

* Unknown which banks are usable as VRAM** The first four 16K bank memory is controlled by OUT [7Fxxh],C0h..DFh instructions. Values C0h..C7h are (probably) usuable as VRAM (working same as on all 64K CPC models)** The next four 16K bank are (hopefully) not usuable as VRAM (for CP/M+ compatibility, which uses them as Work normal CPC6128s. Values C8h..DFh do access the additional RAM)** For further banks it's totally unknown if they are used as VRAM or not* Unknown if it's fully dk'tronics compatible, or more like incompletely implemented Inicron (C8h..D3h when using the cut-down 320K upgrade variant* Unknown what happens on accessing the unused region via OUT [7Fxxh],FCh.).FFh == Memory Configurations ==

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)

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

IF (VCC) /A15S= /A14 * /A15 + ;bank bit1

/A15 * A14 * D2 * /CPU * /MUX + ;bank bit2 /A15 * A14 * D1 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)

IF '''Note:''' For VRAM access, bank bits 2,3,4 are forced to zero (GNDby above formulas) /MUX = /MUX, 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.

IF Some notes on the syntax:* The first two lines assign the pin-outs. Observe that leading "/" slashes are omitted here. For example, "/CPU" (GNDin schematic) becomes "CPU" (in source code). Accordingly "/IOWR=CPU" (in source code) would be double-negated "/IOWR/CPU" aka "CPU" (in schematic).* The "IF (condition) signal== Newer Info == Having a short look at " part means that "signal" becomes an output when condition is true. In the articleabove source code, it seems to be all different as than expected: * There condition is no dk'tronics compatibility intended - howeveralways true (VCC), c't and dk'tronics are based on or, for the CPC6128 banking mechanismlast 2 lines, so they work similar, and to some level there is some always false (unintendedGND) compatibility. Namely* The "*" and "+" operators are meaning "* = AND", ONE HALF of the memory can be accessed "+ = OR". The idea behind that confusing syntax was to make it "easier" to learn for people who are trained only in dk'tronics style fashionbasic maths (the formulas do also work when treating *=multiply, and +=plus. For example: 1+0+1+1 = 3 = nonzero = true). * There seems to must be no hardware based "Video RAM" support at all. However, there's some unspectacular software based example included that copies expansion RAM to VRAM via LDIR opcodepriority 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).

 * [http[CPC_6320_/_CPC_6512_-_internal_320K_/_512K_for_CPC_6128|CPC 6320 / CPC 6512 (by eto) - similar logic, but fully standards compatible]]* [https://cpcwiki.eu/forum/index.php/topic,662.msg7113.html#msg7113 Bank Swapper by Khany/Cherry-T] (less complex: bank-exchanging toggle, no memory expansion; 1993)