SCSI interface signal lines
The SCSI interface uses 18 signal lines:
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| Select (SEL) |
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| Acknowledge (ACK) |
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| Attention (ATN) |
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| Reset (RST) |
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Host |
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| Busy (BSY) |
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Computer |
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| Data | Target | |
Initiator |
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| Data Parity (DB(P)) |
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Control/Data (C/D)
Input/Output (I/O)
Message (MSG)
Request (REQ)
Issuing SCSI commands
There are seven steps or phases for issuing commands to the scanner or controller:
Bus Free
Arbitration
Selection
Command
Data
Status
Message
Bus Free phase — the SCSI bus is not being used by an initiator (host computer) or the target (scanner). No signals on the bus are asserted.
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