Installation manual

Appendix B - Hardware Specifications 59
Cyclades-TS Installation Manual
APPENDIX B HARDWARE SPECIFICATIONS
This chapter has all the information you need to quickly and successfully purchase or build RS-232 cabling. It
focuses on information related to the Cyclades-TS, but most of the information applies to any RS-232 cabling
The RS-232 Standard
RS-232C, EIA RS-232, or simply RS-232 refer to a standard defined by the Electronic Industries Association in
1969 for serial communication. More than 30 years later, we have found more applications for this standard than
its creators could have imagined. Almost all electronic devices nowadays have serial communication ports.
RS-232 was defined to connect Data Terminal Equipment, (DTE, usually a computer or terminal) to Data
Communication Equipment (DCE, usually a modem):
DTE —> RS-232 —> DCE —> communication line –> DCE —> RS-232 –> DTE
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