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REFERENCE
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MM1.memory.hack
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2009-11-06
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84 lines
The MM/1 4 Meg Memory Hack
NOTE: This is NOT a pretty hack. There will be several wires going
around the board, pins with legs sticking up and piggybacked chips. It
is NOT easy to do, so take care and go slow. You'd better be skilled in
doing this sort of thing before attempting it or you can do permanent
damage to your I/O board.
1. Remove the pins from the SIMM socket that connect to WE* (pin 21).
Do this for BOTH sockets.
2. Cut off the tail of the pins as close to the bottom as possible.
3. Solder a wires to each pin and reinsert into the socket so as not make
contact with the board. Wrap the one wire around the side and under the
socket through to the other side. You might want to use a TINY spot
of super glue to hold the pins back in the socket. Pressing a SIMM
in will hold them in place. Make sure the pin no longer contacts the
solder pad underneath by using a continuity checker or VOM.
4. Take a 74AC32 or 74HCT32 and cut pins 6, 8, and 11 off as close to the
chip body as possible. Take pins 12-13, 4-5, and 9-10, and tie them
all to ground (pin 7).
5. If your MM/1 DOES NOT have an accelerator board, then cut pins 11, 12,
and 13 on the 74HC00 in the middle of the I/O board as close to the
board as possible. Pull those pins up.
If you DO have an accelerator board, or are planning on getting one
very soon and don't want to use your computer until then, don't do
this step.
6. Solder a wire from pin 16 of U1 (the 22V10 PAL) on the back side of the
board, wrap it around and solder it to pins 12 and 13 of the 74HC00.
If you have an accelerator board, solder the wire directly to pin 1 of
of piggybacked 74AC32 when it is mounted.
7. Solder a wire to pin 11 of the 74HC00. Not needed on accelerated MM/1s.
8. Piggyback the 74AC32 onto the 74HC00 soldering only Vcc and ground
(pins 7 and 14) to the chip underneath.
9. Solder both the wires from the SIMM socket to pin 3 on the 74AC32.
10. Solder the wire from pin 11 of the 74HC00 to pin 1 of the 74AC32.
On acclerated MM/1s this wire is directly from pin 16 of the PAL.
11. Solder a wire from pin 2 to WE*. A good place to get it is one of
empty holes where you unsoldered the SIMM socket pins.
CHECK ALL YOUR WORK BEFORE APPLYING POWER TO THE SYSTEM!!!
If you plan on running with 1 Meg SIMMs for the time being, just restart
your system and all should work. If it doesn't, start checking your
work. When you plan on using 4 Meg SIMMs, you need to make a new init
module. Take a 3 Meg init module and copy it using a new name to denote
it is a 8 Meg init. Take that init module and modify offset $DF from
$20 to $80. Modify offset $AA from $33 to $38. Make a new bootdisk
using this module. Make sure you identify this as an 8 Meg boot.
Also, you'll need to change the memory setting jumpers on the mother
board to use the full 8 Meg. On a 1 Meg system, the jumper closest to
the backplane is jumpered and the other is not. On a 3 Meg system, both
jumpers are set, on the 8 Meg system, remove the jumper closest to the
backplane and keep the other one on. Just the opposite of the settings
for a one meg system.
You can boot a 3 Meg system using an 8 Meg bootdisk and it will work until
you try to write past the upper memory limit and then crash city. Be aware
of this.
Good luck!
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