🚀 go-pugleaf

RO 3.1 ...
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Locate link 12, and notice hard-wired links. Cut these, place a 2x2 header,
and put jumpers on in opposite direction (1-3 and 2-4 instead of the old
1-2 and 3-4). Then you have to connect the LA19 and LA20 signals to pin 30
and 31 respectively of all the ROMs. Alas, in the A300 these are taken to
5v in one of the power planes, so there's no way of cutting them and rewiring.
What I did was bend pins 30 and 31 on all the ROMs slightly outwards, so
they are 'dangling' just outside the sockets (i.e. uncut, but straight down
because of lack of room to bend them sideways). Then loop the wires, and
connect the 30 wire to pin 17 of IC 28 (which is LA19) and 31 to pin 16
(LA20).

RO2 too ...
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This is more complicated. I piggy-backed the old ROMs on the new ones, cutting
free the CS pins (20/28, i.e. 22/32) and pins 28/28 (which needs 5v). Then
also looped a wire through these, connected 28/28 to 5v, then cut the MROMCS
line. I.e. now only a switch is needed between MROMCS and either of the two
CS lines. Because I'm not a great fan of looping these high-frequency signals
through long wires, I used a 74HCT138 to do the switching, which is
B=C=C2B=0v, C2A=MROMCS, C1=5v, A taken to the switch, to take it to 0v or
5v, and Y0 to CS of the old ROMs, Y1 to the CS of the new ROMs (where MROMCS
was cut).


John Kortink

Student of Informatics at the University of Twente, The Netherlands
(God, will I ever stop doing things 'on the side' and get it done?)
NETMAIL : kortink@cs.utwente.nl              DISCLAIMER : the usual