Serial Interface Operation Revision 3
CDM-760 Advanced High-Speed Trunking Modem MN-CDM760
8–3
8.4 Remote Commands and Queries Overview
8.4.1 Basic Protocol
Whether in EIA-232 or EIA-485 mode, all data is transmitted as asynchronous serial characters, suitable for transmission and reception by a
Universal Asynchronous Receiver/Transmitter (UART). The asynchronous character in the form 8-N-1 (8 data bits, no parity, 1 stop bit). The baud
rate may vary from 1200 to 38400 baud.
All data is transmitted in framed packets. The Controller is in charge of the process of monitor and control, and is the only device that is
permitted to initiate, at will, the transmission of data. Targets are only permitted to transmit when they have been specifically instructed to do
so by the Controller.
All messages from Controller-to-Target require a response, with one exception – this will be either to return data that has been requested by the
Controller, or to acknowledge reception of an instruction to change the configuration of the Target. The exception to this is when the Controller
broadcasts a message (such as Set Time/Date) using Address 0, when the Target is set to EIA-485 mode. In this context, the Carriage Return and
Line Feed characters are considered printable.
8.4.2 Packet Structure
The exchange of information is transmitted, Controller-to-Target and Target-to-Controller, in packets. Each packet contains a finite number of
bytes consisting of printable ASCII characters, excluding ASCII Code 127 (DELETE).
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