Impulse 3604 - Manual (Page 10)

Appendix C – Electrical Interface
Sealevel Systems PC-SIO-232 Page 8
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 or EIA/TIA-232. 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 is 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 at distances less than 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 (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, Data Terminal Equipment (DTE) and Data
Circuit-Terminating Equipment (DCE). The Sealevel Systems adapter is a DTE interface.