Mocomtech CRS-300 operation manual EIA-232, Basic Protocol

CRS-300 1:10 Redundancy Switch	Revision 16
Remote Control	MN/CRS300.IOM

C.3 EIA-232

This is a much simpler configuration in which the Controller device is connected directly to the Target via a two-wire-plus-ground connection. Controller-to-Target data is carried, via EIA-232 electrical levels, on one conductor, and Target-to-Controller data is carried in the other direction on the other conductor.

C.4 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 UART. The asynchronous character format may be selected as: 8-N-1 (8 data bits, no parity, one stop bit). The baud rate may vary between 300 and 19,200 baud.

All data is transmitted in framed packets. The Controller is assumed a PC or ASCII dumb terminal that is in charge of the process of monitor and control. The Controller 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 bytes within a packet are printable ASCII characters, less than ASCII code 127. In this context, the Carriage Return and Line Feed characters are considered printable.

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.

C.4.1 Rules for Remote Serial Communications with the CRS-300

1.Always wait for a response (up to 15 seconds) from the CRS-300 before sending the next query or command.

2.If a "time-out" response ('~') is sent from the CRS-300, the user must resend the previous command.

The ‘~’ response indicates that a pass-through command to a modem/transceiver attached to the CRS-300 has "timed-out" and there was no response from the other device. During this wait, do not communicate with the CRS-300. After the '~' response is sent by the CRS-300, it is now ready to receive a message again. The CRS-300 knows to wait different times for the different messages it is sending to modems:

•Status queries (no commands) are fast, (typically less than 333 ms).

•Configuration changes (commands) take longer and vary by modem type.

•Individual commands responses are faster than those to global commands (MGC). More parameters require more time.

•A pass-through command is passed with little inspection by the switch,but remember the modem being addressed may be at the distant end of an EDMAC link! Types of pass-through commands:

oTo a local modem;

oTo a modem at the distant end (EDMAC);

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