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
[[File:CPC6128.hex]] : Fixed version of Amstrad 40031 GAL replacement, Hex Intel version.
== Initial replacement equation (Porchy) ==
The following equations were worked out by Porchy (member on CPCWiki Forum). These can be used to program replacements:
A15OUT = (!X2 & !X1 & A14
# !X3 & !X2 & A14
# A15);
!X1 = (!A15 & D7ANDD6 & RESET & !IOWR & D0
# !X1 & RESET & IOWR
# !X1 & !D7ANDD6 & RESET
# !X1 & A15 & RESET);
!X2 = (!A15 & D7ANDD6 & RESET & !IOWR & D1
# !X2 & RESET & IOWR
# !X2 & !D7ANDD6 & RESET
# !X2 & A15 & RESET);
!X3 = (!A15 & D7ANDD6 & RESET & !IOWR & D2
# !X3 & RESET & IOWR
# !X3 & !D7ANDD6 & RESET
# !X3 & A15 & RESET);
!CAS1 = (X3 & !X1 & A15 & A14 & !NCAS & !RAMDIS & !CPU & CAS0
# !X3 & !A15 & A14 & !NCAS & !RAMDIS & !CPU & CAS0
# X3 & !X2 & X1 & !NCAS & !RAMDIS & !CPU & CAS0
# !NCAS & CAS0 & !CAS1);
!CAS0 = (X3 & X2 & X1 & !NCAS & !RAMDIS & CAS1
# X3 & !X1 & !A15 & !NCAS & !RAMDIS & CAS1
# !X3 & A15 & !NCAS & !RAMDIS & CAS1
# !X1 & !A14 & !NCAS & !RAMDIS & CAS1
# !X3 & !A14 & !NCAS & !RAMDIS & CAS1
# !NCAS & !RAMDIS & CPU & CAS1
# !NCAS & !CAS0 & CAS1);
A14OUT = (A15 & A14
# !X1 & A14
# X3 & A14);
[[File:Amstrad6128.jed]] Original JED File posted on CPCWiki Forum
== PAL MMR register ==
</pre>
== Note: The CPC 464/664 cannot deal with A14/A15 for Base 64k page like the 6128 does. So external RAM expansions differ in their behaviour regarding &C3 mode. See also ==[https://www.cpcwiki.eu/forum/amstrad-cpc-hardware/464-preasic-c3-ram-configuration-and-rom-7/ Discussion on the forum] and [https://www.cpcwiki.eu/forum/amstrad-cpc-hardware/dk%27tronics-ram-c3-selection-464/ Another discussion]
*CPC 464/664 cannot deal with == Initial replacement equation (Porchy) == The following equations were worked out by Porchy (member on CPCWiki Forum). These can be used to program replacements: A15OUT = (!X2 & !X1 & A14/ # !X3 & !X2 & A14 # A15 for Base 64k page like ); !X1 = (!A15 & D7ANDD6 & RESET & !IOWR & D0 # !X1 & RESET & IOWR # !X1 & !D7ANDD6 & RESET # !X1 & A15 & RESET); !X2 = (!A15 & D7ANDD6 & RESET & !IOWR & D1 # !X2 & RESET & IOWR # !X2 & !D7ANDD6 & RESET # !X2 & A15 & RESET); !X3 = (!A15 & D7ANDD6 & RESET & !IOWR & D2 # !X3 & RESET & IOWR # !X3 & !D7ANDD6 & RESET # !X3 & A15 & RESET); !CAS1 = (X3 & !X1 & A15 & A14 & !NCAS & !RAMDIS & !CPU & CAS0 # !X3 & !A15 & A14 & !NCAS & !RAMDIS & !CPU & CAS0 # X3 & !X2 & X1 & !NCAS & !RAMDIS & !CPU & CAS0 # !NCAS & CAS0 & !CAS1); !CAS0 = (X3 & X2 & X1 & !NCAS & !RAMDIS & CAS1 # X3 & !X1 & !A15 & !NCAS & !RAMDIS & CAS1 # !X3 & A15 & !NCAS & !RAMDIS & CAS1 # !X1 & !A14 & !NCAS & !RAMDIS & CAS1 # !X3 & !A14 & !NCAS & !RAMDIS & CAS1 # !NCAS & !RAMDIS & CPU & CAS1 # !NCAS & !CAS0 & CAS1); A14OUT = (A15 & A14 # !X1 & A14 # X3 & A14); [[File:Amstrad6128.jed]] Original JED File posted on CPCWiki Forum == Fixed version (Gerald) ==Original version from Porchy suffer from a bad handling of the 6128 doesRAMDIS signal. So This cause screen artefact when accessing an external extension RAM expansions differ in their behaviour regarding &C3 modelike XMEM. See 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 ); [https[File://www.cpcwikiCPC6128.eu/forum/amstrad-cpc-hardware/464-preasic-c3-ram-configuration-and-rom-7/ Discussion on the forumJED] and ] : Fixed version of Amstrad 40031 GAL replacement [[httpsFile://wwwCPC6128.cpcwiki.eu/forum/amstrad-cpc-hardware/dk%27tronics-ram-c3-selection-464/ Another discussionhex]] : Fixed version of Amstrad 40031 GAL replacement, Hex Intel version. == See also ==
*[[Gate Array and ASIC Pin-Outs]]
