8 Ground
9 TXD B
10 Control B
11 RXD B
13 Signal timing B
5,7,12,14,15 Not used
19.2.18.3 Functionality
The data format is HDLC. The speed for the transmission of the messages used is 64 kbit/
s.
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.
19.2.18.4 Technical data
Table 711: 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
Section 19 1MRK505222-UUS C
IED hardware
1128
Technical reference manual
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