Changes
[[Category:DIY]] [[Category:Memory expansions]]
A project to upgrade a CPC6128 to 512K RAM (total), done by replacing the CPC6128's RAM chips, and its PAL banking chip, the project was released 1987 in german magazine ''c't Magazin''.
== The Circuit ==
* 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 bank selection for CPU address 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 does also affect bank bits0-1 for VRAM at , but there are several differences:** For the mapping to 4000h..7FFFh; thus the CRTC may see bank 0-3 , 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 that region some (whilstunintended) semi-compatibility, as far as knownbut there's still one big difference: along with the above values, on a normal CPCdk'tronics maps bank 3 to C000h..FFFFh, it should always see whilst c't maps bank 1 in 7 to that region).
== Missing Info Memory Configurations ==
OUT [7Fxxh],C0h+... 0 1 2 3 4 5 6 7 8..31
== 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
IF (GND) /IOWR=/IOWR ;dummy (do not output anything on this pin)
Some notes on the syntax:* There seems to 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 no hardware based double-negated "Video RAM//CPU" support at allaka "CPU" (in schematic). However* The "IF (condition) signal=" part means that "signal" becomes an output when condition is true. In the above source code, there's some unspectacular software based example included 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 copies expansion RAM confusing syntax was to VRAM via LDIR opcodemake it "easier" to learn for people who are trained only in basic maths (the formulas do also work when treating *=multiply, and +=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).
== Scanned Article / Schematics ==
== Related hardware modifications ==
* [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)
* [[CPC4MB| CPC4MB memory upgrade by Yarek]] (more advanced; 2005/2006)