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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 widespread 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 (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.
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© Sealevel Systems, Inc.
7406 Manual | SL9066 7/2021
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