Interface X.21 - Siemens SWT 3000 Equipment Manual

Digital Line Equipment

9.3 Interface X.21

9.3 Interface X.21
The X.21 interface is structured according to the RS422 standard (ITU-T V.11) and consists of the data lines
TxD and RxD and the clock lines TxC and RxC.
[dwx21int-051011-01.tif, 1, en_US]
Figure 9-1
The high transmission reliability of the interface is achieved by evaluating the differential voltage between a
twisted wire pair in each case. The electrical levels of the data lines are defined with 0.3 V to -6 V for logic 1
and with +0.3 V to +6 V for logic 0. The voltage between the measuring points (A) and (B) defines the signal
state.
Terminations of 100 Ω at the receiver inputs not only prevent reflections on the transmission line, but also
contribute to transmission reliability through the resulting pronounced current.
Characteristics:
Number of signal lines:
Levels:
Line run:
Bit rate:
334
Structure of the X.21 Interface
8
For each balanced pair for data and clock pulse, for transmit and receive direction
in each case
< 6 V
Maximum voltage of each line to GND (absolute)
> 2 V
Differential voltage between the lines
Twisted in pairs and shielded, joint shield for all 4 line pairs
64 Kbps
Smart Communication, SWT 3000 Teleprotection, Equipment Manual
C53000-G6040-C605-1, Edition 03.2020