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CONTROL register format

The CPU queries and commands the RAM-DISK device by reading or writing the CONTROL register, which format is as following:

    bit     Meaning
    ----------------------------------
    11      Alarm
    10      Write Protect
    9       Access BC register
    8       Proprietary
    0-7     Partition number
    ----------------------------------

Bits 0-7 hold the current partition number. After writing this byte, every I/O operation on the DATA register will apply to that partition only.

Bit 8 is for proprietary implementation. The RAM-DISK device designer can make free use of it.

Bit 9, when set, makes the next reading or write operation made on the CONTROL register to be effective on the BC register instead. This a the way of getting or setting the current block number.

Bit 10, when set, makes the memory content read-only. Any attempt to write on the DATA register will result in an Alarm shown in the device's panel.

Bit 11 is read-only. It reads 1 if the device is in Alarm condition. It is opt to the software to pay attention or not to this bit.