64kB EEPROM Installation


Static electricity

The module can be destroyed by static electricity. Care should be taken to ground yourself before touching the module or any circuitry in the BBC. Older 74 series logic can be fairly robust to static discharge but CMOS and modern surface mount components are susceptible.

Basic static precautions are simple and free!

Plug in the BBC's mains plug but keep it switched off at the outlet. Then touch the bare metal of the power supply or UHF modulator with a finger. Easy!

Correct orientation

The module can be destroyed by incorrect insertion. Be careful when inserting the module that the pins are aligned correctly and the orientation is correct. Incorrectly inserted/orientated modules may be destroyed and cause damage to your BBC.

Be careful to double check the alignment and orientation when installing upgrades and paged ROMs.






White "BBC B 64KB EEPROM" writing is upright, pin 1 is top left and wires exit towards the front.




Tools needed are a Philips No.2 screw driver to open the case. A Philips or flathead screwdriver (depending on your exact BBC) and a spanner/socket or pliers to remove the keyboard. Tweezers or fine needle nose pliers.

  1. Open the BBC case. Two (large) crosshead screws underneath at the front and two at the back. The lid then hinges up and off at the back.
  2. Remove the bolts holding in the keyboard.
  3. Lift and pull the keyboard forward to expose the ROM sockets (front right). You do not need to disconnect the keyboard wire but may if you want better access.
  4. Connect one long clip wire to the left most pin labelled ROMSEL. Connect the second long clip wire to the right most pin labelled WDS. Note which colour wire you connected to which signal. Tweezers make it easy to push the connectors on to the header.
  5. Insert the module in a free ROM socket. The pin marked PIN1 should be top left and the writing on the module the correct way up when viewed from the front of the computer. The wires should come out underneath towards the keyboard. (You should not need much force to push the module into the socket - check the pin alignment if it doesn't go in easily.)
  6. Connect the ROMSEL spring clip to IC26 (left of the CPU) pin 5. (Pin 1 is top left count anticlockwise). See photo.
  7. Connect the WDS spring clip to IC73 (under analogue port) pin 24. (Pin 28 is top right count clockwise). See photo.
  8. Bolt keyboard back in and close case.

Accidentally connecting the spring clips to the wrong pins will not cause harm to the module. If the spring clips are disconnected then the EEPROM will not work properly and only the high ROM image will be visible but the BBC may well boot. Check that the spring clips do not short circuit to the adjacent pins.

Short jumper wires are provided to connect WDS and ROMSEL between multiple modules.

Getting started

The EEPROM modules come pre-loaded with a simple BASIC language Paged ROM Tool (RT) to program the boards stored using the Acorn ROM filesystem.

You should copy the RT to another filing system. The following example shows how to copy RT to disc.


Run the RT after loading with RUN from the BASIC prompt or CHAIN "RTOOL".

The interactive RT lists all the ROMs, EEPROMs and sideways RAM you have installed. Press ? to display help.

Manually erasing an EEPROM the from RT menu erases all 64kB. i.e. all four 16kB paged ROM banks. You do not need to manually erase the EEPROM before programming.

After changing ROM images loaded you must reset the computer either from the RT menu or by pressing BREAK. This forces the operating system to rescan the ROMs. The OS may crash the computer if it tries to execute code from a ROM you just erased for example!

The EEPROM chips are OK for 100,000 erase/write cycles typically according to the manufacturer. This is enough to reprogram it ten times a day for 27 years straight!


If installing multiple modules connect the central ROMSEL and WDS headers to the 2nd board with the short jumper wires provided.

If IC26 or IC73 are inconvenient then alternate pins for the clips can be used.

  • IC26 pin 5 (74LS139 left of 6502 CPU)
  • IC76 pin 9 (74LS163 under keyboard ribbon cable)
  • IC73 pin 24 (uPD7002 next to analogue port)
  • IC77 pin 8 (74LS00 near the copyright logo where it says the issue number)
  • IC78 pin 10 (8271 above keyboard connector)