GAL16V8
MIXSID1

MS /IO1EN /IO2EN RW   /CS  /IO2 /IO1 A5 A8 GND
PS CSI1   CSO1   CSI2 CSO2 /CS2 /CS1 NC NC VCC

CSO1 = MS * CS +
      /MS * CS * /A5 * /A8
      
CSO2 = MS * CS * /RW +             
      /MS * CS * A5 +
      /MS * CS * A8 +
      /MS * IO1EN * IO1 +
      /MS * IO2EN * IO2

CS1 = PS * CSI1 +
      /PS * CSI2

CS2 = PS * CSI2 +
      /PS * CSI1

DESCRIPTION:

MixSID chip select logic
Compile with GALasm (https://github.com/daveho/GALasm)

A0, A1, A5, A8, IO1, IO2, RW, CS  = C64 input signals
MS, PS, IO1EN, IO2EN              = control signals
CS1, CS2                          = chip select outputs

CSO1, CSO2 -> connect externally to CSI1, CSI2

MS = MODE SELECT:

   HIGH = PARALLEL, BOTH SIDS AT D400-D800
   LOW  = STEREO, SID1 AT $D400, SID2 AT D420, D500, DE00*, DF00*
   * (only if IOn is connected and IOnEN=low)
   
IO1EN, IO2EN = IO ENABLE lines

   HIGH: Prevent SID2 at the corresponding address
   LOW:  Second SID also at the corresponding address

PS = PRIORITY SELECT:

   HIGH: Normal Priority, SID1 always $d400, SID2 maybe stereo
   LOW:  Swapped Priority, SID1 may be stereo, SID2 always at $d400