LSI 53C810A User Manual

Page 91

5-17

Register: 0x08 (0x88)

SCSI First Byte Received (SFBR)
Read/Write

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)