J058 SCRAM
The SCRAM is a peripheral board which plugs into the bus of an STEbus computer system. It has storage for up to 48K (49152 Bytes) of data, and has a Real-Time Clock/calendar. Both memory and clock are maintained on power-down for several weeks by an on-board backup battery. During the transition between battery and external power, a special voltage-sensing and opto-isolating circuit is used to prevent corruption of data.
The board contains six sockets each capable of accepting 8K or 2K devices; either EPROMs or CMOS RAM chips. Depending on the devices used, the board has a total capacity of either 12K or 48K and this is locatable in any 16K or 64K block in the entire STE memory map. For maximum flexibility, the board need not be fully populated, and the board can then be set to respond only to addresses corresponding to the sockets in use. Each socket can be individually jumpered to accept EPROMs or RAM, so that the SCRAM can carry all system memory onboard.
The Real Time Clock/Calendar is capable of remembering and updating Hours, Minutes, Seconds, Day of the week and Date, and has full alarm and interrupt facilities. It is I/O mapped, and contains 50 Bytes of extra RAM which are also maintained on power-down. It can be located anywhere in the STE I/O map, and for systems where I/O space is at a premium the board can be linked to ignore 16, 32 or the full 50 bytes of the extra memory, and leave only the RTC registers.