Avago Technologies LSI53C876E - Manual (Page 132)

4-38 Registers
LSI Logic SDMS software uses the GPIO0 pin to toggle
SCSI device LEDs, turning on the LED whenever the
LSI53C876 SCSI function is on the SCSI bus. SDMS
software drives this pin low to turn on the LED, or drives
it high to turn off the LED.
LSI Logic software also uses the GPIO[1:0] signals to
access serial EEPROM. GPIO1 is used as a clock, with
the GPIO0 pin serving as data.
Register: 0x08
SCSI First Byte Received (SFBR)
Read/Write
1B SCSI First Byte Received [7:0]
This register contains the first byte received in any
asynchronous information transfer phase. For example,
when a LSI53C876 SCSI function is operating in initiator
mode, this register contains the first byte received in the
Message-In, Status, and Data-In phases.
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 SFBR as the destination. This
allows bit testing after an operation.
The SFBR is not writable using the CPU, and therefore
not by a Memory Move. However, it can be loaded using
SCRIPTS Read/Write operations. To load the SFBR with
a byte stored in system memory, the byte must first be
moved to an intermediate LSI53C876 SCSI function
register (such as the SCRATCH register), and then to the
SFBR.
7 0
1B
0 0 0 0 0 0 0 0