Retries; Baud Rate, Stop Bits, Parity, Response Time-Out, Ack/Nak Handshake; Errors; Things To Remember When Using Ssi Communication - Motorola Symbol MS4404 Integration Manual

8 - 6 Symbol MS4404/MS4407 Integration Guide

Retries

When sending data, the host resends 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 the serial parameters, the ACK response to the PARAM_SEND uses the
previous values for these parameters. The new values take effect for the next transaction.

Errors

The decoder generates 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

If not using hardware handshaking, space messages sufficiently apart. The host must not communicate with the
decoder if the decoder is sending.
If 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. Temporary changes are lost when you remove
power from the decoder. Permanent changes are written to non-volatile memory. Frequent changes shorten the life
of the non-volatile memory.