ICS Advent COMM4AT/EX, Product Manual

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Manual Number: 00750-123-1 Page 17
Appendix B: Electrical Interface
RS-232
Quite possibly the most widely used communication standard is RS-232. This implementation has
been defined and revised several times and is often referred to as RS-232-C/D/E or EIA/TIA-232-
C/D/E. It is defined as “ Interface between Data Terminal Equipment and Data Circuit- Terminat-
ing Equipment Employing Serial Binary Data Interchange ”. The mechanical implementation of
RS-232 is on a 25-pin D sub connector. The IBM PC computer defined the RS-232 port on a 9 pin
D sub connector and subsequently the EIA/TIA approved this implementation as the EIA/TIA-574
standard. This standard has defined as the “ 9-Position Non-Synchronous Interface between Data
Terminal Equipment and Data Circuit-Terminating Equipment Employing Serial Binary Data In-
terchange” . Both implementations are in wide spread use and will be referred to as RS-232 in this
document. RS-232 is capable of operating at data rates up to 20K bps / 50 ft. The absolute maxi-
mum data rate may vary due to line conditions and cable lengths. RS-232 often operates at 38.4K
bps over very short distances. The voltage levels defined by RS-232 range from -12 to +12 volts.
RS-232 is a single ended or unbalanced interface, meaning that a single electrical signal is com-
pared to a common signal (ground) to determine binary logic states. A voltage of +12 volts (usually
+3 to +10 volts) represents a binary 0 (space) and -12 volts (-3 to -10 volts) denote a binary 1
(mark). The RS-232 and the EIA/TIA-574 specification define two types of interface circuits D ata
T erminal E quipment ( DTE ) and D ata C ircuit-Terminating E quipment ( DCE ). The COMM4AT/
EX Adapter is a DTE interface.