Connect a wire from TP10 to LKS1 pin 4.
Remove IC8 and bend pins 1, 2 and 3 (carefully) out straight so that they
will clear the socket and replace IC8.
Remove IC71 and do the same with pin 8.
Connect a wire from IC71/8 to IC8/2.
Touch solder a wire onto IC24/12 and connect the other end to IC8/1.
Touch solder a wire onto IC18//13 and connect the other end to
The effect of this mod is only to provide a chip select and a RAMDIS
signal when the tape drive is on. Certainly on my machine, it is always on
when powered up so SIMON is connected in and any RAM in the system occupying
those addresses is disabled. Once SIMON is entered other than for booting up
or once CP/M is loaded and started, port 0 is reset and SIMON disappears from
the memory map. Plug in and power up and all should be as before (on a 60k max
CP/M) provided SIMON is not used as a monitor. If the system is powered up
without a disk in drive A, your machine will crash once port 0 is reset by
Before a full 64k system can be installed, the cold boot loader must be
modified to switch out SIMON before loading the CP/M system. To do this,
perform the following sequence of operations:
Use MOVCPM to generate a 64k system. Allow room for SYS if you use it.
Save the result as CPM64.COM.
Load CPM64.COM under DDT or ZSID.
Use the S command to modify the addresses given below to the values
090B 18 097C 3E
090C 6C 097D 01
0979 AF 097E 18
097A D3 097F 8D
Use ^C or G0 and save the modified CPM64.COM.
Use SYSGEN to put the file on drive A. This can be done by typing:
after which, specify drive A as the destination.
Unplug & plug in again with the new system in the A drive and Hey Presto,
you should have a 64K system up and running with no SIMON in the way. As
an added bonus, it won’t get in the way when paging RAM either.
Faulty RAM Board
My second bit of first-aid is probably of no use to Kevin Weatherhead who
has, by now, probably cured his faulty RAM board himself. If not then here
Kevin doesn’t say which type of RAM board he is using, so I shall go into
& B boards and the Gemini
64k RAM card. The problem is
this. When Kevin powers up, his RAM card is full of rubbish as expected. He
can write zeros to the card but not ones. Fortunately, all three RAM cards use
the same principle so only a brief “how it works” is necessary.
When the Z80 wants to read data, the address lines contain the required
address. This address is decoded by the RAM cards to select the appropriate
RAM chips. The /WR signal from the Nasbus/80-bus provides the /WR signal to
the RAM chips so that they accept data rather than send it. This signal will
be a ‘1’ when reading and this side appears to work. As Kevin can also write
to the chips, albeit in a limited fashion, this appears to be switching
correctly. Data to be written to the RAM chips is gated into the RAM after