After the target detects the BSY signal is true, it shall also assert the |
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BSY signal and wait at least two deskew delays and then release the |
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SEL signal. The target may then change the I/O signal and the |
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DATA BUS. After the reselected initiator detects the SEL signal is |
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false, it shall release the BSY signal. The target shall continue |
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asserting the BSY signal until it relinquished the SCSI bus. (See |
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ANSI | INTERFACE |
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 3.6). 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.
The information transfer phases use one or more REQ/ACK handshakes to control the information transfer. Each REQ/ACK handshake allows the transfer of one byte of information. During the information transfer phases the BSY signal shall remain true and the SEL signal shall remain false. Additionally, during the inforamtion transfer phases, the target shall continuously envelope the REQ/ACK handshake(s) with the C/D, I/O, and MSG signals in such a manner that these control signals are valid for a bus settle delay before the assertion of the REQ signal of the first handshake and remain valid until after the negation of the ACK signal at the end of the handshake of the last transfer of the phase.
M3099GX/GH OEM Manual |