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10-30
SE955 Integration Guide
Communication Summary
RTS/CTS Lines
All communication must use RTS/CTS handshaking as described in
ACK/NAK Option
ACK/NAK handshaking can be enabled or disabled. This handshaking is enabled by default; disabling this is not recommended as it
can lead to communication problems, since handshaking is the only indication that a message was received and if it was received
correctly. ACK/NAK is not used with unpacketed decode data regardless of whether or not this option is enabled.
Number of Data Bits
All communication with the decoder must use eight bit data.
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. Both the host and decoder should use the same value for this parameter.
A temporary change may be made to the Serial Response Time-out when the host takes longer to process
an ACK, or longer data string. Frequent permanent changes are not recommended due to limited write cycles
of non volatile memory.
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 uses the previous values
for these parameters. The new values then take effect for the subsequent 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.
Appendix A, Serial Interface
Specification.
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