8 - 6 DS8178 Digital Scanner Product Reference 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 digital scanner.
Retries
When sending data, the host should resend twice after the initial send if the digital scanner 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 digital scanner replies with a NAK RESEND, the host resends the data. All resent
messages must have the resend bit set in the Status byte.
The digital scanner 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 digital scanner issues a communication error when:
•
The CTS line is asserted when the digital scanner 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 digital scanner if the digital scanner 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 digital scanner
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. Zebra does not recommend frequent permanent changes due to limited write cycles
of non-volatile memory.
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