Appendix J - Rs-232C Interface Specifications - Multitech MultiModem II BA-Series User Manual

MultiModemBA User Guide

Appendix J - RS-232C Interface Specifications

The modem's RS-232C interface circuits have been designed to meet the electrical specifications
given in EIA (Electronic Industries Association) RS-232C standards. All signals generated by the
modem are approximately 10 volts when measured across a load of 3000 ohms or greater. The
receiving circuits of the modem will accept signals in the 3 to 25 volt range. The voltage thresholds
are:
Negative = voltage more negative than 3 volts with respect to signal ground
Positive = voltage more positive than +3 volts with respect to signal ground
SIGNAL INFORMATION:
Binary State
Signal Condition
Control and Timing Function
The input impedances of all modem circuits which accept signals from the data processing terminal
or CPU equipment have DC resistances of 4.7K. For more specific details, consult the EIA RS-232C
standard itself.
The following chart lists the EIA RS-232C interface pins and circuits present on the modem's
RS232C Interface connector. All other pins are unused.
Pin
Assignment
1
2
3
4
5
6
7
8
9**
12
15***
17***
20
22
24
25
** Pin 9 need not be present in your RS-232C cable
*** Pins 15 and 17 are necessary only for synchronous operation
**** Also known as DTR (Data Terminal Ready)
The computer or terminal should be supplied with a cable terminated with a Cinch DB-25P (or
equivalent) connector mounted in a Cinch DB-51226-1 (or equivalent) hood assembly as specified by
the EIA RS-232C standard.
156
NEGATIVE
One
Mark
Off
Designation eia
circuit
PG --
SD BA
RD BB
RTS CA
CTS CB
DSR CC
SG AB
CD CF
+v +v
HS --
TC DB
RC DD
TR**** CD
RI CE
XTC DA
OOS CN
POSITIVE
Zero
Space
On
CCITT signal Function
circuit source
101 -- Protective Ground
103 DTE Transmitted Data
104 DCE Received Data
105 DTE Request to Send
106 DCE Clear to Send
107 DCE Data Set Ready
102 -- Signal Ground
109 DCE Carrier Detect
-- DCE Test Voltage
-- DCE High Speed
114 DCE Transmit Clock
115 DCE Receive Clock
108/2 DTE Terminal Ready
125 DCE Ring Indicator
113 DTE External Transmit Clock
142 DTE Terminal Busy