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Spare ROM/RAM cartridges for the Master and Electron

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Background

Both the Master 128 and the Electron (with a 'Plus 1' expansion fitted) members of the BBC Microcomputer range include 44 pin edge connectors to accept a number of 3rd party upgrade cartridges including genlock adapters; speech synthesisers; RAM expansions and extra sideways ROMs.

By far the most common are the ROM/RAM cartridges which allow easy loading and removal of extra memory without having to take the lid off the machine, overcoming the limited number of sockets on the main PCB and approaching the operating system limit of a maximum of 16 sideways banks at once.

However, actually finding a supply of cartridges has become increasingly difficult as they have often become lost or damaged over the years.

Fortunately the design for a ROM/RAM cartridge is simplicity itself, requiring only minimal chip select logic, because the expansion card interface is almost a raw copy of the 6502's system bus.

Cartridge
The ROM/RAM cartridge with DOSFS fitted

Features and capabilities

The board contains some new features which are not normally associated with existing cartridges, noticeably:

While the official ROM cartridges also came in matching a beige plastic case, the cartridges offered here further reduce complexity by making the PCB the shape of the cartridge itself - thus eliminating expensive plastic tooling costs. This also means that no screwdrivers are required to dismantle and change the chips over.

In the default configuration the cartridge behaves like the original Acorn adapter, though the extra functionality requires the changing of one or more of the onboard 3 option links:

L1: L2: L3: Comments:
North North North IC1=8k ROM, 16k ROM
IC2=disabled
North North South IC1=32k RAM (Master only)
IC2=disabled
North South North IC1=8k ROM, 16k ROM
IC2=8k ROM, 16k ROM
North South South Invalid combination
South North North IC1=32k ROM, half 64k ROM
IC2=disabled
South North South Invalid combination
South South North Invalid combination
South South South Invalid combination

Links
Survey of link positions

Boards use high quality turned pin IC sockets to reduce strain when inserting and removing devices, and to improve contact reliability over leaf style IC sockets.
The card edge fingers are gold plated to reduce contact resistance and oxide build up which would otherwise lead to poor contact and unreliability.


Electron users

An unexpanded Acorn Electron will first need a 'Plus 1' expansion fitting to the rear of the main unit. This adds an analogue port for joysticks, a printer port, and two cartridge slots. Therefore up to 4 x 16k ROMs can be added to the machine.

Cartridge
In use with the Plus 1 expansion for the Acorn Electron

The cartridge slot nearest the keyboard provides ROM numbers 2 & 3, and the cartridge slot at the back of the case provides ROM numbers 0 & 1. Please note that when used with an Acorn Electron the cartridge cannot be configured with the 32k RAM option because the read/write signal (on cartridge connector pin A11) is wired differently to a BBC Master, therefore only ROM chips may be used.


Availability

Orders can be placed online, or alternatively sent by post.

These cartridges are available now, and are offered in various different options depending on the application:

Option: Price: Comments:
Default configuration
£19.20 inc postage
With L1=N; L2=S; L3=N
Supplied with instruction leaflet
32k RAM configuration (Master only)
£24.20 inc postage
With L1=N; L2=N; L3=S
Complete with 62256 low power SRAM
Supplied with instruction leaflet
Non default configuration
£1.00 per change
Custom link changes
Only applies at time of supply
Please allow an extra 7 days for delivery

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