Adaptor to enable 32-pin EPROM to be used in BBC Master
This page describes how to build an adaptor, so that the 1 megabit ROM
may be replaced with an EPROM device. This enables a fix to be made for the
Y2000 problems with the BBC Master computer,
or to alter the set of ROM images.
The 1 megabit ROM used in the BBC Master computer is a 28-pin device, but
128K × 8 EPROMs (e.g. 27C010) are 32-pin devices and so can't
be plugged directly into the BBC Master:
|1 megabit ROM||27C010 EPROM|
An adaptor is needed, let's make one.
Thanks to Jonathan Graham Harston, there's now a wiring diagram for the adaptor.
This shows the 32 pin EPROM in the middle, with the two halves of the 28 pin
ROM socket either side:
The 28-pin Turned Pin IC socket will plug in to the existing socket in the
BBC Master Computer. A Turned Pin socket is chosen to cause little deformation
of the contacts in the original socket.
- 1 off 32-pin Wirewrap IC socket
- 1 off 28-pin Turned Pin IC socket
- Some hook-up wire
- 20 minutes or so
The 32-pin wirewrap socket provides physical support to the adaptor.
Now remove the MOS ROM from the socket in the BBC Master Computer, and plug
the adaptor in its place. An appropriately programmed EPROM, when fitted
into the 32-pin socket, will provide the Operating System firmware for the computer.
- Align the 32-pin socket to that the lower 28 pins align with
the buckets on the top faces of the 28-pin socket.
- Solder all the left hand wirewrap pins into the corresponding
buckets on the 28-pin socket (i.e. pins 3 to 16 on the 32 pin
socket are connected to pins 1 to 14 on the 28-pin socket).
- Cut pins 1,2,24,30,31,and 32 of the 32-pin socket to about half length
- Solder all the full length pins on the right hand side of the
wirewrap socket to the corresponding buckets on the 28 pin
socket (i.e. pins 17 to 23 on the 32-pin socket are connected
to pins 15 to 21 on the 28-pin socket, and pins 25 to 29 on
the 32-pin socket are connected to pins 23 to 27 on the 28-pin
- Connect pin 2 of the 32-pin socket to pin 22 of the 28-pin socket
- Connect pin 32 of the 32-pin socket to pin 28 of the 28-pin socket
- Connect pins 1 and 24 of the 32-pin socket to pin 16 of the
- Connect pin 31 of the 32-pin socket to pin 32 of the 32-pin socket
A guide to the order of the ROM images in the 1 megabit ROM, and how to
capture the images whilst the 1 megabit ROM is still in the BBC Master,
forms part of my BBC Master 128 and Y2000 page.
Information supplied by Andrew Benham (G8FSL), Southgate, London N14 4XD,
Mail Andrew Benham (email@example.com)