Date   : Sun, 29 Mar 2009 00:41:53 +0000
From   : jgh@... (Jonathan Graham Harston)
Subject: A quick question about EPROM programming

Ian Tonks wrote:
> I suppose I have a related question, can I drop in a 27512 for example, tell
> the programmer it's a 27128 and expect it to work like one? Obviously I
 
To be safe you'd have to program both 16Ks of the EPROM with the
same data as you wouldn't know which half would get selected once
it was in the computer. Most programmers that can program 16K
EPROMs can also program 32K ones, often you program each 16K half
at a time. If the programmer doesn't support programming 32K
EPROMs, you can do it manually with a wire link.
 
Drop the EPROM into the ZIF socket, but ensure pin 27 does not go
into the socket. Connect a wire link between the free pin 27 and 0v
to program the bottom 16K, and to +5v to program the top 16K. *DO*
*NOT* put a wire link into pin 27 of the ZIF socket as when
programming a 16K EPROM that pin has 12v/21v at it.
 
If the above does not work, then the programmer is not supplying a
programming voltage at pin 1, so in addition to the above you would
have to ensure pin 1 doesn't go into the ZIP socket and use a link
to connect pin 1 to the socket for pin 27 to pick up the
programming voltage.
 
See, it's a bit fiddly. Ideally, use a programmer that knows about
32K EPROMs.
 
Anyway, using using a flying lead, you can use a 32K EPROM in a BBC
to hold two 16K images, see http://mdfs.net/Info/Comp/BBC/SROMs/32K
 
-- 
J.G.Harston - jgh@...                - mdfs.net/User/JGH
PDP-11 BBC BASIC development - http://mdfs.net/PDP11/BBCBasic/blog