Changes
New PLD version fixing screen corruption when using external ram extension
On the CPC 6128 schematic, it is top centre: [http://www.cpcwiki.eu/imgs/4/4a/CPC6128_Schematic.png CPC6128 Schematic] however the X inputs aren't distinguished.
== Fixed version (Gerald) ==
Original version from Porchy suffer from a bad handling of the RAMDIS signal. This cause screen artefact when accessing an external extension RAM like XMEM.
A14OUT = !( !A14
# !A15 & !Q0 & Q2 );
A15OUT = !( !A15 & !A14
# !A15 & !Q1
# !A15 & !Q0 & !Q2 );
Q0 = ( D7ANDD6 & nRESET & D0 & !A15 & !nIOWR
# !D7ANDD6 & nRESET & Q0
# nRESET & A15 & Q0
# nRESET & nIOWR & Q0 );
Q1 = ( D7ANDD6 & nRESET & D1 & !A15 & !nIOWR
# !D7ANDD6 & nRESET & Q1
# nRESET & A15 & Q1
# nRESET & nIOWR & Q1 );
Q2 = ( D7ANDD6 & nRESET & D2 & !A15 & !nIOWR
# !D7ANDD6 & nRESET & Q2
# nRESET & A15 & Q2
# nRESET & nIOWR & Q2 );
nCAS0 = ( nCAS
# RAMDIS & !nCPU & nCAS0
# !A15 & A14 & !nCPU & Q2 & nCAS0
# A15 & A14 & !nCPU & Q0 & !Q2 & nCAS0
# !nCPU & !Q0 & Q1 & !Q2 & nCAS0
# !nCAS1 );
nCAS1 = !( !RAMDIS & !nCAS & !A15 & A14 & !nCPU & Q2 & nCAS0
# !RAMDIS & !nCAS & A15 & A14 & !nCPU & Q0 & !Q2 & nCAS0
# !RAMDIS & !nCAS & !nCPU & !Q0 & Q1 & !Q2 & nCAS0
# !nCAS & !A15 & A14 & Q2 & nCAS0 & !nCAS1
# !nCAS & A15 & A14 & Q0 & !Q2 & nCAS0 & !nCAS1
# !nCAS & !Q0 & Q1 & !Q2 & nCAS0 & !nCAS1 );
[[File:CPC6128.JED]] : Fixed version of Amstrad 40031 GAL replacement
== Initial replacement equation (Porchy) ==
The following equations were worked out by Porchy (member on CPCWiki Forum). These can be used to program replacements:
