Comtech EF Data RSU-503 - Manual (Page 63)

Remote Control Operation RSU-503 Redundancy Switch Unit
B–2 Rev. 8
B.1 General
Remote controls and status information are transferred via an RS-485 (optional RS-232)
serial communications link.
Commands and data are transferred on the remote control communications link as
US ASCII-encoded character strings.
The remote communications link is operated in a half-duplex mode.
Communications on the remote link are initiated by a remote controller or terminal. The
switch never transmits data on the link unless it is commanded to do so.
Serial communications with either RFT through the switch remains the same as
communicating directly with the unit. Each individual RFT is assigned its own unique
address, and will respond when that address is polled. To the RFT, the interconnection is
transparent—it will not know whether the command came through the switch or directly
from the terminal.
The switch receives all commands from the interface, decodes the contained address,
compares it to its stored addresses, and routes the message to the intended destination.
When an RFT communication parameter (address, baud rate, and parity) is changed, the
switch will also store that information in its EEPROM.
Note: All three units must have unique addresses.
B.2 Message Structure
The ASCII character format used requires 11 bits/character:
•
1 start bit
•
7 information bits plus 1 parity bit
•
2 stop bits
or:
•
1 start bit
•
8 information bits with no parity bit
•
2 stop bits
Messages on the remote link fall into the categories of commands and responses.
Commands are messages which are transmitted to the switch, while responses are messages
returned by the switch in response to a command.