Motorola Symbol PL4507, Integration Manual

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6 - 6 Symbol PL4507 Decoder Integration Guide
Serial Response Time-out
The Serial Response Time-out parameter determines how long to wait for a handshaking response before trying
again, or aborting any further attempts. Set the same value for both the host and decoder.
Retries
When sending data, the host should resend twice after the initial send if the decoder does not respond with an ACK
or NAK (if ACK/NAK handshaking is enabled), or response data (e.g., PARAM_SEND, REPLY_REVISION). If the
decoder replies with a NAK RESEND, the host resends the data. All resent messages must have the resend bit set
in the Status byte.
The decoder resends data two times after the initial send if the host fails to reply with an ACK or NAK (if ACK/NAK
handshaking is enabled).
Baud Rate, Stop Bits, Parity, Response Time-out, ACK/NAK Handshake
If you use PARAM_SEND to change these serial parameters, the ACK response to the PARAM_SEND uses the
previous values for these parameters. The new values then take effect for the next transaction.
Errors
The decoder issues a communication error 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
When not using hardware handshaking, space messages sufficiently apart. The host must not communicate with
the decoder if the decoder is transmitting.
When using hardware handshaking, 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. Removing power from the decoder discards
temporary changes. Permanent changes are written to non-volatile memory. Frequent changes shorten the life of
the non-volatile memory.
NOTE You can temporarily change the Serial Response Time-out when the host takes longer to process an ACK
or longer data string. Motorola does not recommend frequent permanent changes due to limited write
cycles of non-volatile memory.