Protocol Operation - Unitech MR350 MKII Technical Reference Manual

Negative ACK
Terminal Transmissions
Transmission
Terminal Data
Acknowledgment
Negative ACK

5.4.1. Protocol Operation

The terminal protocol operates as a multi-point stop and wait
protocol. A station sends only one frame and then stops and waits for
a response.
The following scenarios typify link transmissions:
* Terminal has no data for the host:
=> STX ADDR
<= EOT - if no data is ready for transmission
* Terminal has data for the host:
=> STX ADDR
<= STX <data> CS1 CS2 ETX - if data is ready
=> ACK
NAK
* The host sends a command to and receives a response from
the terminal in one poll cycle; it then acknowledges receipt of
the terminal command response:
=>
<=
<=
=>
NAK
Format
STX, data, CS1, CS2, ETX
ACK
NAK
- if data is received correctly, or
- if an error has occurred
STX, CMD, parms, ... CS1, CS2, ADDR
ACK - if data is received correctly and no response is
required, or
NAK - if an error occurred or if there is response data
to be sent.
Command response and data:
ACK - if a command response was sent from the
terminal and received correctly by the host, or
NAK - if an error occurred in the command response
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