19
VHSI Port Interface Specifications
The X.21 Interface
The pin-out assignments for the X.21 interface
are shown in the following diagram.
The signal definitions and names are listed in
Table 9 below.
VHSI—X.21 Connections
The wiring diagram below shows the connections required to construct a
VHSI—X.21 cable. For the additional information required to construct your
own cables, see “VHSI Cable Construction Information” on page 10.
Figure 15: VHSI—X.21 Connections
Pin #
Signal
Name
Direction
CCITT #
1/15
PGND
Protective Ground
Common
101
2
T(A)
Transmit Data (+)
Output
103A
3
C(A)
Control Signal (+)
Output
105A
4
R(A)
Receive Data (+)
Input
104A
5
I(A)
Indication (+)
Input
109A
6
S(A)
Signal Element Timing (+)
Input
115A
7
B(A)
Byte Timing (+)
Input
114A
8
SGND
Signal Ground
Common
102
9
T(B)
Transmit Data (-)
Output
103B
10
C(B)
Control Signal (-)
Output
105B
11
R(B)
Receive Data (-)
Input
104B
12
I(B)
Indication (-)
Input
109B
13
S(B)
Signal Element Timing (-)
Input
115B
14
B(B)
Byte Timing (-)
Input
114B
Table 9: X.21 Interface Signals
Figure 14: X.21 Interface
PG N D
1
T(A)
C(A)
R(A)
I(A)
S(A)
B(A)
SGND
T(B)
C(B)
R(B)
I(B)
S(B)
B(B)
PG N D
15
8
9
VHSI
X.21
1
19
4
22
5
23
6
24
8
26
11
29
12
12
3
30
10
8
1
9
7
14
4
11
6
13
5
TWISTED PAIRS
(MANDATORY)
2
DRAIN WIRE
BRAID
