User guide

ASCOM USER GUIDE
High Speed Base Band Modems
59
8.5.2 Module Link Settings
J1 – V.36 Circuit 103 (Transmit data) Circuit Termination – This link connects a 120 ohm load
resistor across the 103 circuit in position 1-3. This helps maintain signal rise times and
minimises reflections at greater than 9.6kbps over long lines. At lower rates and over short
lines the termination resistor may be omitted, (link set position 1-2).
J2 – V.36 Circuit 113 (External Signal Element Timing) Circuit Termination – This link connects
a 120 ohm resistor across the 113 circuit in position 1-3. This helps maintain signal rise times
and minimises reflections at rates greater than 9.6kbps over long lines. At lower rates and
over short lines the termination resistor may be omitted, (link set position 1-2).
J1
Interface Module -
Top View
J2
2
1
3
3
1
2
8
58 ASCOM USER GUIDE
High Speed Base Band Modems
8.4.3 External Timing
If External timing is required i.e. the modem is to be used as a DTE then a change over cable
will be required as shown in the diagram below.
8.5 X.21 BIS (V.36)
8.5.1 37 Way D-type V.36 Connector pin allocation
Pin Type SITS
Unbal A-wire B-wire Circuit Description 89/43
19,20,27, 102 Common Return Common
29,31
4 22 103 Transmitted Data Load
6 24 104 Received Data Generator
7 25 105* Request to Send Load
9 (9) (27) 106* Ready for Sending Generator
11 (11) (29) 107* Data Set Ready Generator
13 (13) (31) 109* Data Channel Received Generator
17 35 113 External Transmitter Signal Element Timing Load
5 23 114 Transmitter Signal Element Timing Generator
8 26 115 Receiver Signal Element Timing Generator
14 140 Remote Loopback Load
10 141 Local Loopback Load
18 142 Test Indicator Generator
7 102 7 102
2 103-A 2 103-A
14 103-B 14 103-B
3 104-A 3 104-A
16 104-B 16 104-B
4 105-A 4 105-A
19* 105-B 19* 105-B
8 109-A 8 109-A
10* 109-B 10* 109-B
24 113-A 17 115-A
11 113-B 9 115-B
Master
High Speed
Modem
Set to
External
Bit Timing
Timing
Source