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Register: 0xFC00
Current SCSI Data (CSD)
Read Only
7
x
x
DB[7:0]
Current SCSI Data
The Current SCSI Data register is a read only register
that allows the microcontroller to read the active SCSI
data bus. Whenever a 1 is read in one of these bits, the
corresponding data signal is asserted on the SCSI bus.
If parity checking is enabled, the SCSI bus parity is
checked at the beginning of the read cycle. This register
is used during arbitration to check for higher priority
arbitrating devices. Parity is not guaranteed valid during
arbitration.
Register: 0xFC00
Output Data (ODR)
Write Only
7
x
x
DB[7:0]
SCSI Output Data
The Output Data register is a write only register that is
used to send data to the SCSI bus. This register is also
used to assert the proper ID bits on the SCSI bus during
the arbitration and selection phases. Writing a 1 to one
of these bits causes the corresponding data signal to be
asserted on the SCSI bus. This register is only asserted
on the SCSI bus when the ADB bit (0xFC01, bit 0) is set.
DB[7:0]
Default:
x
x
DB[7:0]
Default:
x
x
x
x
x
x
1
x
[7:0]
1
x
[7:0]
4-3
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