Communication Protocol
Communication is carried out in units of bytes in the following procedure. When the computer sends one byte of data, it waits for a return from the VTR before sending the next byte. The return from the VTR may not only be one byte of data, but can be multiple bytes of data. For a command, such as EJECT, which takes time to execute, not only the return immediately after receipt of the command is issued, but a return indicating the result of execution upon completion of operation is also issued. The command, the return from the VTR, and parameters are all defined as the command in the
Commands to operate the VTR
When a command (CMD) has no parameter:
CMD
RxD 3AH
TxD 0AH
RET
When a command (CMD) has parameters (PARAM.):
| CMD | PARAM. | PARAM. | ||||
RxD | 3AH |
| 3AH |
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| 3AH |
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TxD 0AH 0AH 0AH
RET RET RET
There are three kinds of returns from the VTR: ACK, NAK, and ERROR.
ACK: Returned when data is correctly returned.
NAK: Returned when communication error is detected or an unidentified command is received.
ERROR: Returned when a command cannot be executed because of tape slack and other errors.
Commands to sense VTR status
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| RxD |
| DAH |
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| C7H |
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| 0AH |
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| ACK |
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Commands from the VTR to the computer to notify of completion of an operation
This return is issued when execution of the following commands is completed: EJECT, FRAME SEARCH, T/D SEARCH, and ALARM SEARCH.
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| RxD | 2AH |
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| TxD |
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| 03H |
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| RET |
| CASSETTE | |||
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| OUT | ||
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There are three kinds of return from the VTR: COMPLETION, NOT TARGET, and CASSETTE OUT.
COMPLETION: Returned when command execution is correctly completed.
NOT TARGET: Returned when the target point specified by the command cannot be found.
CASSETTE OUT: Returned when the cassette is ejected.
Extended commands
A command consists basically of one byte. Some commands may function when combined with another command.
Extended Secondary
CMD CMD
RxD | DAH |
| CAH |
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TxD 0AH 31H
RET RET
Notes
•Do not send the next command before receiving the return from the VTR.
If the return from the VTR is not received within 10 msec or more after the transmission is completed, appropriate processing must be executed because the communication is judged not executed correctly.
•Do not send any other command between the extended command and the secondary command.
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