RFL SMX3 / 21
Page 6 of 22
Issue 1.4
User Manual
08 June 2009
6. X.21 Aggregate Port
The X.21 port is a DB15 male connector; this is connected internally to a header on
the PCB using a ribbon cable. The X.21 port may be configured as DTE or DCE by
fitting the ribbon cable to the appropriate X.21 Port Header, and by selecting settings
on DIP switch 5.
Note:
DTE is the standard configuration, and is used in all
applications where the network provides the signal timing.
Transceivers are specified to ± 15kV IEC1000-4-2 air discharge ESD protection and
port connections are additionally protected by Tranzorb type arrays.
This port carries an aggregate of three bi-directional data channels; one X.21
channel and two V.24 channels.
Standard X.21 Port Pin-out (when in DTE configuration) – D15M on chassis
Circuit
Pin A
Pin B
Direction
Notes
T Transmit
Data
2
9 Output
R Receive
Data
4
11 Input
C Control
3
10 Output Permanently
on
I Indication
5
12 Input
Signal
ignored
S
Signal Element
Timing
6
13
Input
Timing signal derived from
the network
G Ground
8
15
X Signal
Element
Timing
7
14
Output
Timing signal transmitted to
network (X). Special applications
only. Requires to be enabled
using mode DTE + Timing X
enabled
Screen / Drain
Must be earthed to shell
X.21 (DTE)
X.21 (DCE)
X.21
V24
X.21 header locations
Headers connected
to X.21 Port
Standard header location
DCE header location only
used when SMX3/40
provides signal timing
