6-39
Simple Serial Interface
Baud Rate, Stop Bits, Parity, Response Time-out, ACK/NAK
Handshake
If the serial parameters above are changed using PARAM_SEND, the ACK response to the
PARAM_SEND is sent using the previous values for these parameters. The new values then
take effect for the next transaction.
Errors
A communication error is generated by the decoder when:
•
The CTS line is asserted when the decoder tries to transmit, and is still asserted on
each of 2 successive retries
•
Failure to receive an ACK or NAK after initial transmit and two resends.
Things to Remember When Using SSI
Communication:
If hardware handshaking is not being used, messages should be spaced sufficiently apart, and
the host must not communicate with the SE-923 if the SE-923 is sending.
If hardware handshaking is used, frame each message properly with the handshaking signals.
Do not try to send two commands within the same handshaking frame.
There is a permanent/temporary bit in the PARAM_SEND message. Temporary changes are
lost when power is removed from the SE-923. Permanent changes are written to non-volatile
memory. Frequent changes shorten the life of the non-volatile memory.
Do not scan parameter bar codes and send parameters via SSI simultaneously. All parameters
can be accessed via SSI, so parameter bar code scanning should not be necessary.
Содержание SE 923
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Страница 236: ...Index 4 SE 923 Scan Engine Integration Guide...
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