MV1A PALs

The MVS boards have two [PAL] PAL20V8H-15 chips which are used to provide some of 's functions. If any of them fails, the board certainly won't start up.

They can be replaced with new or working chips programmed with the following JEDEC files:

=SNK1A= Does some address decoding. Pin 1 might be AS instead of RW.



JEDEC file:


 * /VPA = /i1 & A20 & A21 & A22I & A23I (Access Fxxxxx, interrupt ack cycle, signal 68k that we need an autovectored interrupt)
 * /WRAMCS = /i1 & A20 & /A21 & /A22I & /A23I (Access 1xxxxx, work RAM)
 * /o17 = /i1 & A20 & /A22I + /i1 & /A22I & A23I + /i1 & A22I & /A23I (Access x0x1 or 10xx (8xxxxx-Bxxxxx) or 01xx (4xxxxx-7xxxxx))
 * /o18 = /i1 & A20 & /A21 & A22I & A23I (Access Dxxxxx, backup RAM)
 * /DIPRD0 = /i1 & /A17 & /A18 & /A19 & A20 & A21 & /A22I & /A23I & /MGA53 & MGA52 (Read 0011000x, must be 300000-31FFFF LDS)
 * /IN3 = /i1 & A17 & /A18 & /A19 & A20 & A21 & /A22I & /A23I & /MGA53 & MGA52 (Read 0011001x...)
 * /o21 = /i1 & A17 & /A18 & /A19 & A20 & A21 & /A22I & /A23I & /MGA51 & MGA52 (Read 0011001x...)
 * /SDW = /i1 & A17 & /A18 & /A19 & A20 & A21 & /A22I & /A23I & MGA51 & /MGA52 (Write 0011001x, must be 320000-33FFFE UDS)

=SNK1B= Generates the signal.



JEDEC file:


 * o17 = /i5 & rf21 + /i5 & i11 + /i6 & rf21 & i23 + /i6 & i14 & rf22 + /i6 & i14 & i23 + /i2 & /i6 & /i14 & /i23
 * DTACK = i3 & i7 & i8 & i9 & i10 & /o17 & /rf21 + i3 & i4 & i7 & i8 & i9 & i10 & /o17
 * /rf20 = i4 & i5 & i6
 * /rf21 = i4 & i5 & i6 + /rf20
 * /rf22 = /rf21 + i4 & i5 & i6