Appendix C - Electrical Interface
PMS8232 / PMS4232 Page
10
Appendix C - 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- Terminating 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 20K bps / 50 ft. The absolute maximum 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 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)
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
PANACOM Technology Adapter is a DTE interface.