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 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 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 used, space messages sufficiently apart. The host must not communicate with the
decoder if the decoder 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 decoder. Permanent changes are written to non-volatile memory. Frequent changes shorten the
life of the non-volatile memory.