Internal RegistersThe RAM-DISK device must have the following internal registers:
DATA (12 bits) Represents the data path to the content.
CONTROL (12 bits) Report status, accepts commands and hold current partition number.
BC (12 bits) Block Count: Holds the current block being accesses.
WC (8 bits ) Word Count: Counts words within current block.
The effective address within the partition is given by BC (most significant 12 bits) and WC (least significant 8 bits). The partition number adds 8 more significant bits for a total address of 28 bits.
When reading or writing continuously on register DATA, register WC is auto-incremented with each read or write operation. Register BC is auto-incremented when WC rolls-over. When count is set on register BC, register WC is automatically reset to zero.
The partition number is never auto-incremented or altered in any way other than over-writing it in the CONTROL register with a write operation.
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
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11 Alarm
10 Write Protect
9 Access BC register
8 Proprietary
0-7 Partition number
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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.
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