SLH85@cc.usu.edu (02/14/90)
A couple of days ago I read a message about piggybacking RAM chips onto the ones already in my 1040ST. It mentioned connecting a single line into the MMU. Is this possible, and if so which line on the MMU should I connect to. Thanks. Kurt Olsen (SLH85@CC.USU.EDU)
pfg@ukc.ac.uk (P.F.Gisby) (02/16/90)
You should not realy 'PIGGY BACK' RAM chips on a 1040 as the process was
designed to upgrade a 520st to a 1040. (I was taught how to do this upgrade
by a technician and you need a very small tipped iron to do it)
To do it on a 1040 you need to do a bit more than just take one line
to the MMU. As you already have the two banks of RAM the line has already
been used. To upgrade a 1040 to 2.5 (or even 4mb) was someting I looked into
for a very long time, as I was continualy running out of RAM in my 1040.
However Uncle Jack made the MEGA 4 so I got one.
The internal structure (I.E. MMU and GLUE) of the MEGA is the same as the 1040
so you can access up to 4mb of RAM in any ST (up until the STE which can access
8mb). Some say you can upgrade to 16mb but Where would you fit the RAM in the
memory map???. If you could the the case would lie that you can upgrade a 520
to a 16mb machine.
Anyway back to the question......
To upgrade a 1040 is NOT as easy as upgrading a 520. First (You don't have
to do this it's just safer, and it gives you 16 4256's to upgrade you friends
520st) you must remove a whole bank (YES ALL 16) of your RAM chips. This is
not a task to be taken lightly as the quality of all circuit boards are very
low so you could break you board without meaning to. Then you must get the
pinouts of the 1 megabit chips that you are going to use. These cost an
awfull lot of money over here in England. After this you MUST (or at least
you may find it easier to fix if it dies, if you do) is put in DIL sockets
in the place of the 4256's. Then comes the fun bit with loads of beding
up pins and wiring them to different places using wire-wrap wire (The pins
that you will need to connect to are mentioned below). Then comes testing
If you've done it right you will have 2.5mb of RAM. If you've done it wrong
OOPPSS and see if you have connected them to the right pins (I.E. DATA) and cut
the three tracks that come from the pins you use on the MMU. There was a
letter going round on how to do this which was quite good and if anyone has it
could they repost it!!!
CONNECTIONS:
MMU PIN 63 MAD8 : memory address data pin 8 (This gives a memory size of 1mb/b)
MMU PIN 64 MAD9 : memory address data pin 9 (This gives a memory size of 2mb/b)
Then you must connect your row and column address stobe lines up, these will
vary depeding on which bank you change. There are 2 column lines and 1 row
line.
The pins that you need to connect up on the RAM chips should be ducumented
where you buy them.
No one to my knoledge has ever tried putting 1mb on one bank before so I think
it can not be done.
GOOD LUCK.
Pete.
(UKC at CANTERBURY. IN THE PHYSICS LAB)
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