PAL16L8

The CPC6128 second bank of 64K RAM is controlled by a PAL 16L8 chip. It has the Amstrad part number 40031.

On the CPC 6128 schematic, it is top centre: CPC6128 Schematic however the X inputs aren't distinguished.

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