SSI Interface
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Serial Response Timeout
The Host Serial Response Timeout parameter determines how long to wait for a handshaking response before
trying again or aborting further attempts. Set the same value for both the host and scanner.
Retries
The host resends data twice after the initial send if the 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 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 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 Timeout, ACK/NAK Handshaking
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 scanner issues a communication error when:
• The CTS line is asserted when the scanner tries to transmit, and is still asserted on each of two successive
retries
• The scanner does not receive an ACK or NAK after initial transmit and two resends.
SSI Communication Notes
• When not using hardware handshaking, space messages sufficiently apart. The host must not
communicate with the scanner if the scanner is transmitting.
• When using hardware handshaking, frame each message properly with 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 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 Host Serial Response Timeout 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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