Table 23: Pinout for the X.21 communication connector
Pin number Signal
1 Shield (earth)
2 TXD A
3 Control A
4 RXD A
6 Signal timing A
8 Earth
9 TXD B
10 Control B
11 RXD B
13 Signal timing B
5,7,12,14,15 Not used
5.4.3 Functionality
GUID-4512904E-08D1-47EC-B005-E66170CEB130 v4
The data format is HDLC. The speed for the transmission of the messages used is 64 kbit/s.
A maximum of 10 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 Hitachi Energy devices.
5.4.4 Technical data
GUID-83EC40D0-ABCF-4292-B3DF-155C3A556B76 v4
Table 24: 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 10 m
Section 5 1MRK505382-UEN Rev. K
Communication set-up
70 Communication set-up, 670/650 series
Application Guide
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