Manual Number: 00750-903-2
Page 15
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-Termi-
nating 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 Interchange”
. 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 20 Kbps / 50 ft. The
absolute maximum data rate may vary due to line conditions and cable lengths. RS-232 often operates
at 38.4 Kbps 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
compared to a common signal (ground) to determine binary logic states. A voltage of +12 volts
(u3 to +10 volts) represents a binary 0 (space) and -12 volts (-3 to -10 volts) denotes 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
adapter is a DTE interface.
