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© Sealevel Systems, Inc. 3603 Manual | SL9111 7/2021
Appendix D - 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 widespread 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 (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, Data Terminal Equipment (DTE) and Data
Circuit-Terminating Equipment (DCE). The Sealevel Systems adapter is a DTE interface.
