Register: 0x08 (0x88)

SCSI First Byte Received (SFBR)

Read/Write

7

0

IB

0

0

0

0

0

0

0

0

This register contains the first byte received in any asynchronous information transfer phase. For example, when the a LSI53C810A is operating in initiator mode, this register contains the first byte received in Message-In, Status phase, Reserved-In and Data-In.

When a Block Move instruction is executed for a particular phase, the first byte received is stored in this register, even if the present phase is the same as the last phase. The first byte received value for a particular input phase is not valid until after a MOVE instruction is executed.

This register is also the accumulator for register read-modify-writes with the SCSI First Byte Received (SFBR) as the destination. This allows bit testing after an operation.

The SCSI First Byte Received (SFBR) cannot be written using the CPU, and therefore not by a Memory Move. Additionally, the Load instruction cannot be used to write to this register. However, it can be loaded using SCRIPTS Read/Write operations. To load the SCSI First Byte Received (SFBR) with a byte stored in system memory, the byte must first be moved to an intermediate LSI53C810A register (such as the SCRATCH register), and then to the SCSI First Byte Received (SFBR).

This register also contains the state of the lower eight bits of the SCSI data bus during the Selection phase if the COM bit in the DMA Control (DCNTL) register is clear.

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LSI 53C810A technical manual Register 0x08, Scsi First Byte Received Sfbr Read/Write