The 8K CMOS RAM Board

Acorn System 8K CMOS RAM

"The CMOS RAM card gives 8K bytes of non-volatile RAM which can be used to store data that is retained when the system is switched off. The card is a 100mm x 160mm Eurocard and connects to the standard Acorn bus using a 64-way connector. A +5V supply is all that is required.

On the card are 16 CMOS RAM ICs which provide a contiguous two blocks of memory, address decoding links allow these two blocks to be memory mapped from any even block boundary, e.g. 0000, 2000, 4000 (hex). Address and data bus buffers then interface the memory ICs to the Acorn bus. A 3.6v battery provides the minimal current requirement of the RAMs so that they hold their data when the +5v goes down. This battery is charged up from the +5v supply when it is on.

Data retention will be at least 60 days. As soon as the +5V begins to go down the bus buffer chips are disabled stopping invalid data from being stored in the RAMs by a dying CPU. There is also provision for an external power fail signal which can be driven from a mains failure detector off the card. Finally there is provision for a write protect switch and a card isolate switch which puts the card into power down mode prior to unplugging it from the Acorn system. Using this, the card can be used to transfer data between systems."






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