User guide

Appendix C – Electrical Interface
Sealevel Systems COMM+232.PCI Page 11
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 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. 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 COMM+232.PCI
is a DTE device.