Specifications

RS-232/422/485 2-PORT PCI CARD, OPTO-ISOLATED

Appendix B. Electrical Interfaces

B.1 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 DB9 connector, and

subsequently the EIA/TIA approved this implement-

ation 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. (15.2 m). 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: DTE and DCE. The PCI Card is a DTE device.