Understanding the Communications Data Display
The information in the Data Display follows the DFS protocol. For every blue Send message, there should be one or more green Reply messages. A Send message without a matching Reply is a clear indication of a problem preventing the station from answering.
The following figure shows an example of one Send/Reply transaction:
As shown, each Send message will be bracketed by two non-printing characters (the square boxes). Each Reply ends with a single box symbol. You should disregard these non-printing characters in the following guide to the codes.
The first two characters in each message are the address of the DFS RTU. (Again, disregard the boxes.) Looking at the examples, you should see that for every Reply following a Send, these two leading characters match.
One exception to the above is the case of a “ZZ” command in the Send message. This indicates that a group poll is being requested, starting at the address appearing in the 5th and 6th character places of the Send field. The following Replies can be seen to include a series of RTU addresses.
A second exception to the above is the case of a station with a Digipeat path. In this case, the Send will start with the address of the station it is repeating through, followed by ‘RD’ and then the station address of the RTU being polled.
The third character in the Send message is the module number. Here, “1” will indicate module A, “2” indicates module B and so on, except for “R” which indicates a Radio module.
There is one exception to this pattern: A “0” in the third character position of the Send indicates that a Full Station Read is being requested. All modules in the station should reply with their status, where an “x” will indicate “No Change” and a “y” will indicate “Change”.
Normally if a reply indicates that there has been a change, a Send request will go to that module to request its new value.
The final character in either a Send or Reply is a check-bit. This may be any printing character, including punctuation. This is the only character in either the Send or Reply that should ever have punctuation: a character other than a letter or number in any other position is a sign of communication errors.