Page B-2
Appendix B — RS232
INTER-TEL
®
AXXESS
®
MANUAL VERSION 11.0 – May 2008
Introduction
1. INTRODUCTION
NOTE: RS232 has undergone several revisions over the last 30 years. The most current ver-
sion of RS232 is EIA/TIA-232-E (July 1991), which includes the alternate use of RTS Running
H/F 2-and CTS as character-by-character hardware flow control signals. The Inter-Tel
®
system
serial ports conform to RTS/CTS flow control per EIA/TIA-232-E. Older versions of RS232, such
as EIA-232-D (1987) and RS232-C (1969) are a subset of EIA/TIA-232-E. Hence, serial ports
which conform to EIA/TIA-232-E are compatible with all RS232-C serial ports. However, if the
RS232-C serial port does not support RTS/CTS flow control, then the connection cannot use
RTS/CTS hardware flow control.
1.1 Connecting two different devices using RS232 can be very confusing as well as time
consuming. The confusion arises because there are so many different factors that can vary on
each type of RS232 connection, such as:
• Type of device
— DTE (Data Terminal Equipment), e.g., PC Serial COM port, Printer, etc.
— DCE (Data Circuit-Terminating Equipment), e.g., modems
• Type of connector
— D-sub (a.k.a. “DB”)
— Modular
• Male or female gender of connector
• Number of pins
— 25 pin DB
—9 pin DB
— 8 pin modular
— 6 pin modular
— 4 pin modular
• Different Cables
— 25 wire straight-through cable
— 9 wire straight-through cable
— Reversing vs. non-reversing modular line cords
— 4-wire, vs. 6-wire vs. 8-wire modular line cords
— Custom cables
— Cable length
• Special Adapters
— 9-to-25 pin adapters
— “Null-modem” adapters
— Gender changers
— Custom adapters
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