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4.3.5 INFORMATION TRANSFER phases
Note:
The COMMAND, DATA, STATUS, and MESSAGE phases are all grouped
together as the information transfer phases because they are all used to transfer
data or control information via the DATA BUS. The actual content of the
information is beyond the scope of this section.
The C/D, I/O, and MSG signals are used to distinguish between the different
information transfer phases (see Table 4.5). The target drives these three signals
and therefore controls all changes from one phase to another. The initiator can
request a MESSAGE OUT phase by asserting the ATN signal, while the target can
cause the BUS FREE phase by releasing the MSG, C/D, I/O, and BSY signals.
Table 4.5 INFORMATION TRANSFER phase type
Phase C/D I/O MSG DB7 to 0, P Transfer direction
DATA OUT 0 0 0 Data INIT TARG
DATA IN 0 1 0 Data INIT TARG
COMMAND 1 0 0 Command INIT TARG
STATUS 1 1 0 Status INIT TARG
* 0 0 1
* 0 1 1
MESSAGE OUT 1 0 1 Message INIT TARG
MESSAGE IN 1 1 1 Message INIT TARG
* : Reserved for future standardization
0: False
1 True
INIT: Initiator
TARG: Target
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