Table of Contents
Advertisement
CRS-311 1:1 Redundancy Switch
Serial-based Remote Product Management
6.2.2 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.
6.2.3 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 from 8‐N‐1 (8 data bits, no parity, one stop bit), 7‐E‐2 (7 data bits,
even parity, 2 stop bits) or 7‐O‐2 (7 data bits, odd parity, 2 stop bits). 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.
6.2.3.1
Rules for Remote Serial Communications with the CRS-311
1. Always wait for a response (or up to 15 seconds) from the CRS‐311 before sending the next query or command.
2. If a "time‐out" response ('~') is sent from the CRS‐311, you must resend the previous command.
The '~' response indicates that a pass‐through command to a modem/transceiver attached to the CRS‐311 has "timed‐out" and
there was no response from the other device. During this wait, do not communicate with the CRS‐311. After the '~' response is
sent by the CRS‐311, it is now ready to receive a message again. The CRS‐311 knows to wait different times for the different
messages it is sending to modems:
6–3
Revision 7
MN/CRS311.IOM
Advertisement
Table of Contents
