10 Jun
2001
10 Jun
'01
8:35 a.m.
My own approach would probably be different, i.e. I'd attempt to use the board
itself, but minimize the amount of hardware required to make it work. If the
board was intended to be used as an 8K board, I'd have to decide whether to make
it into a 64K board or to leave it as an 8K board, but since, in the original
poster's case, it was an 8K (?) board with 1K devices he couldn't conveniently
program, I'd say he'll be happy with an 8K board when he's done.
My own preference would be for using a single site and putting either an 8K
EPROM or BBRAM (with a physical switch on the nWrite line) in that site and
being done with it. Once you have the board, the BBRAM is the way to go, since
you don't really need a programmer.
BTW, 2716-compatible BBRAMs are quite common, though the 2716's are less so.
Dick
----- Original Message -----
From: "Tony Duell" <ard(a)p850ug1.demon.co.uk>
To: <classiccmp(a)classiccmp.org>
Sent: Sunday, June 10, 2001 1:45 PM
Subject: Re: EPROM replacement and other helpful hints, was Re: IMSAI
Sure, I was trying to keep it simple for the non-electronics-experts here.
If you're going to us a DIP switch, then the best way to do it is to wire
one section of the DIP swtich between an 'extra' address line and ground.
Connect a 10k resistor (or thereabouts, this is not critical) between the
'extra' address line and +5V. You will need a DIP switch with at least 3
on/off (form A, SPST) sections (get a 4 section one and ignore the last
switch) and 3 10k resistors.
Then you have have 8 1K blocks of code in the 2764, and select them using
the DIP switch. It means you can have 8 attempts at writing the code
before you have to erase the EPROM.
But if you're just trying to replace a 2708, and you have the code and
you know it works, you don't need to bother with this. Stick the code in
the first 1024 locations of the 2764 and tie A10, A11 and A12 to ground.
-tony
top 3 address lines (A10--A12). Assuming you burn
the code into the
lowest 1K locations of the EPROM ,then simply connect those 'extra'
address lines to ground. That will mean only the bottom 1K of the EPROM
is ever accessed which is what you want.
I would be tempted to use a dip switch, then you could dump a bunch of code
and bank switch it.