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Appendix B
RS232C Interface Specification
The MultiMux RS232C interface circuits have been designed to meet the electrical specifications given in the EIA
(Electronic Industries Association) RS232C and CCITT (Consultative Committee of International Telegraph and
Telephone) standards. All signals generated by the mux are approximately 10 volts when measured across a load of
300 ohms or greater. The receiving circuits of the mux 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: NEGATIVE POSITIVE
Binary State One Zero
Signal Condition Mark Space
Control and Timing Function Off On
The input impedances of all mux 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 RS232C standard itself.
The following chart lists the EIA RS232C interface pins and circuits present on the mux RS232C interface connector.
All other pins are unused. The composite side of the mux is configured as a DTE device and the channel sides are
DCE devices.
PIN MULTI-TECH EIA CCITT SIGNAL CIRCUIT
ASSIGNMENT DESIGNATION CIRCUIT CIRCUIT SOURCE* FUNCTION
2 SD BA 103 DTE Transmitted Data
3 RD BB 104 DCE Received Data
4 RTS CA 105 DTE Request to Send
5 CTS CB 106 DCE Clear to Send
6 DSR CC 107 DCE Data Set Ready
7 SG AB 102 Signal Ground
B CD CF 109 DCE Data Carrier Detector
9 +V +V -- DCE Test Voltage
15 TC DB 114 DCE Transmit Clock
17 RC DD 115 DCE Receive Clock
20 TR CD 108/2 DTE Data Terminal Ready
22 Rl CE 125 DCE Ring Indicator
24 XTC DA 113 DTE External Transmit
25 OOS CN 142 DTE Terminal Busy
*DTE =Data Terminal Equipment
DCE=Data Communications Equipment
The computer or terminal should be supplied with a cable terminated with a Cinch DB25P (or equivalent) connector mounted in a Cinch
DB51226-1 (or equivalent) hood assembly as specified by the RS232C/V.24 standard.