CONTREX MLP-Trim - Manual (Page 116)

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Communications Software Design
The MLP–Trim Serial Communications Interface uses a polling technique to establish a
link with the host computer. With the exception of Keypad Lockout (CP-98), all of the
Control Parameters and Monitor Parameters that are accessible through the MLP–
Trim's front panel keypad are also accessible through the Serial Communications
Interface. The host computer sends a twelve character record to the MLP–Trim to
establish the link and the MLP–Trim responds with either a conformation or an error
message. Once the MLP–Trim responds, the host computer can send additional
transmissions.
All of the MLP–Trim's messages use the USA Standard Code for Information
Interchange (ASCII). The host computer sends three types of messages;
Parameter Send - To change CPs.
Control Command Send - To control operating states.
Data Inquiry - To monitor CPs and MPs.
These three message types, their character level descriptions in binary and ASCII, as
well as the MLP–Trim's response record, are outlined in the sections that follow.