Comtech EF Data CRS-200 REDUNDANCY SWITCH User Manual

Page 46

CRS-200

COMTECH COMMUNICATIONS CORPORATION

CRS-200 REDUNDANCY SWITCH - OPERATIONS MANUAL PAGE 44

12.3 RS232

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

RS232 electrical levels, on one conductor, and target-to-controller data is carried in the other

direction on the other conductor.

12.4 BASIC PROTOCOL

Whether in RS232 or RS485 mode, all data is transmitted as asynchronous serial characters,

suitable for transmission and reception by a UART. In this case, the asynchronous character

format is fixed at 8 data bits, one stop bit, no parity. The baud rate may vary between 300

baud and 19,200 baud.

All data is transmitted in framed packets. The controller is assumed to be 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 RS485 mode.

12.5 PACKET STRUCTURE

Controller-to-target:

Start of

Target

Address

Instruction

Code

Optional

End of Packet

Packet

Address

De-limiter

Code

Qualifier

Arguments

= or ?

Carriage

ASCII code

ASCII code 47

ASCII code

Return ASCII

61 or 63 (1

code 13

(1 character)

(4 characters)

(1 character)

(3 characters)

character)

(n characters)

(1 character)

Example: <0000/RSH=30{CR}