ABB Relion REG670, Technical Manual, Page: 1201 / 1298

A maximum of 100 meter of cable is allowed to ensure the quality of the data
(deviation from X.21 standard cable length).
Synchronization
The X.21 LDCM works like a DTE (Data Terminal Equipment) and is normally
expecting synchronization from the DCE (Data Circuit Equipment). The transmission
is normally synchronized to the Signal Element Timing signal when a device is a DTE.
When the signal is high it will read the data at the receiver and when the signal is low
it will write data to the transmitter. This behaviour can be inverted in the control
register.
Normally an external multiplexer is used and it should act like the master.
When two X.21 LDCM is directly communicating with each other one must be set as
a master generating the synchronization for the other (the slave). The DTE Signal
Element Timing is created from the internal 64 kHz clock.
The Byte Timing signal is not used in ABB devices.
21.2.16.4 Technical data
Table 925: Galvanic X.21 line data communication module (X.21-LDCM)
Quantity Range or value
Connector, X.21 Micro D-sub, 15-pole male, 1.27 mm (0.050") pitch
Connector, ground selection 2 pole screw terminal
Standard CCITT X21
Communication speed 64 kbit/s
Insulation 1 kV
Maximum cable length 100 m
21.2.17 GPS time synchronization module (GTM)
21.2.17.1 Introduction
This module includes a GPS receiver used for time synchronization. The GPS has one
SMA contact for connection to an antenna. It also includes an optical PPS ST-
connector output.
21.2.17.2 Design
The GTM is a PCMIP-format card and is placed only on one of the ADM slots. The
antenna input connector is shielded and directly attached to a grounded plate to
eliminate the risk of electromagnetic interference.
1MRK502052-UEN B
Section 21
IED hardware
1195
Technical manual