Appendix C - Example Link Level Exchanges (Serial Communications and USB emulating Serial)

Normally the POS and Simplify respond to each message received with an ACK (followed by the response message, if any).

If a corrupted message (bad LRC) is received, the response is a NAK. The POS device should attempt to transmit the message a parameterized number of times before assuming communications are lost.

Normal message flow with all ACKs. See text above.

Message flow with ACKs and one NAK See text above.