Service manual

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Installation & Service Manual
Appendix B - Hardware Specifications and Cabling
Cyclades-TS
RS-232 is now mostly being used to connect DTE devices directly (without modems or communication lines in
between). While that was not the original intention, it is possible with some wiring tricks. The relevant signals (or
wires) in a RS-232 cable, from the standpoint of the computer (DTE) , are:
Receive Data (RxD) and Transmit Data (TxD) – The actual data signals
Signal Ground (Gnd) - Electrical reference for both ends
Data Terminal Ready (DTR) - Indicates that the computer (DTE) is active
Data Set Ready (DSR) - Indicates that the modem (DCE) is active.
Data Carrier Ready (DCD) - Indicates that the connection over the communication line is active
CTS (Clear to Send, an input) – Flow control for data flowing from DTE to DCE
RTS (Request to Send, an output) – Flow control for data flowing from DCE to DTE
Not all signals are necessary for every application, so the RS-232 cable may not need all 7 wires.
The RS-232 interface defines communication parameters such as parity, number of bits per character, number
of stop-bits and the baud rate. Both sides must be configured with the same parameters. That is the first thing to
verify if you think you have the correct cable and things still do not work. The most common configuration is 8N1
(8 bits of data per character, no parity bit included with the data, 1 stop-bit to indicate the end of a character).
The baud rate in a RS-232 line translates directly into the data speed in bits per second (bps). Usual transmission
speeds range between 9,600 bps and 19,200bps (used in most automation and console applications) to 115,200
bps (used by the fastest modems).
Cable Length
The original RS-232 specifications were defined to work at a maximum speed of 19,200 bps over distances up
to 15 meters (or about 50 feet). That was 30 years ago. Today, RS-232 interfaces can drive signals faster and
through longer cables.
As a general rule, consider:
• If the speed is lower than 38.4 kbps, you are safe with any cable up to 30 meters (100 feet)
• If the speed is 38.4 kbps or higher, cables should be shorter than 10 meters (30 feet)