Richard Erlacher wrote:
Would anyone be able to help me with this VECTOR GRAPHICS 64K DRAM BOARD's
switch settings? The signals seem to be OK, but no data propagates from
the thing. I'm not anxious to count through the combinations of
settings.
According to the schematics for the Rev-3 board, S1 is the Bank Select with
positions 0 - 7 (or probably labeled 1 - 8) corresponding to D0 - D7. D0 -
D7 go through 74175 Quad D latches and come out on the Not Q outputs. These
are then all anded together (U41 - 74ls30) to output the Bank Select signal.
Hmmm, interesting, it looks like the inputs are left floating when the
switch is open, and I have a hard time believing that with LS type
circuitry.
There is a note indicating:
Jumper Memory Enabled
1 to 3 0000h - FFFFh
5 to 3 0000h - DFFFh
4 to 3 0000h - BFFFh, E000h - FFFFh
2 to 3 0000h - BFFFh