Appendix b - rs-232c interface specification – Multi-Tech Systems DataTalker DT101/xx User Manual
Page 119

119
Appendix B - RS-232C Interface Specification
Appendix B - RS-232C Interface Specification
The DataTalker's RS232C interface circuits have been designed to meet the electrical
specifications given in the EIA (Electronic Industries Association) RS232C and ITU-T
(International Telecommunications Union) V.24 standards. All signals generated by the
DataTalker are approximately 10 volts when measured across a load of 300 ohms or greater. The
receiving circuits of the DataTalker 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 DataTalker 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 DataTalker’s
RS232C connector. All other pins are unused. The composite side of the DataTalker is configured
as a DTE device and the channel sides are DCE devices.
PIN
MULTI-TECH
EIA
CCITT
SIGNAL
CIRCUIT
ASS
DESIG
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 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.