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Table 4-1.
Information Transfer Phases
--I
SIGNAL
I
MSG
I
C/D
I
I/O
3
0
0
3
0
1
0
1
0
3
1
1
1
0
0
1
3
1
1
1
0
1
1
1
NOTES:
3
1
INIT
ACB-5533
PHASE NAME
DATA OUT
DATA IN
COMMAND
STATUS
Reserved
Reserved
MSG OUT
MSG IN
--_
..
= SIGNAL DEASSERTION
= SIGNAL ASSERTION
= INITIATOR
= TARGET
DIRECTION OF
INFORMATION XFER
(INIT to ACB-5533)
(ACB-5533 to INIT)
(INIT to ACB-5533)
(ACB-5530 to INIT)
(INIT to ACB-5533)
(ACB-5533 to INIT)
The INFORMATION TRANSFER phases use the REQ/ACK handshake to
control data transfer.
Each REQ/ACK allows the transfer of one
byte of data.
The handshake starts with the Target asserting the
REQ signal.
The Initiator responds by asserting the ACK signal,
indicating a byte transfer. The Target
th~n
deasserts the REQ
signal and the Initiator responds by deasserting the ACK signal.
with I/O signal asserted, data will be input to the Initiator
from
the ACB-5530.
The ACB-5500 ensures
that valid data
is
available on the bus (at the Initiator port) before the assertion
of R E Qat the In i t i at
0
r po r t.
Th e d a t a r em a ins val i dun til the
assertion of ACK by the Initiator.
The Initiator must ensure
that data has been read from the bus before asserting ACK.
The
ACB-5530 compensates for cable skew and the skew of its own
drivers.
The ACB-5533 always guarantees good parity on inbound
data transfers.
With the I/O signal not asserted, data will be output from the
Initiator to the ACB-5533.
The Initiator must ensure valid data
on the bus (at the Target port) before the assertion of ACK on
the bus.
The Initiator should compensate for cable skew and skew
of its own drivers.
Valid data must remain on the bus until the
ACB-5530 deasserts REQ.
The ACB-5503 will optionally check
parity on the outbound data transfers.
503534-30
4-6
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