Communication solutions for power utilities
1U SHELF TYPE MAS-2
WITH ASYNCHRONOUS PROGRAMMABLE MODEM MAFP - Rev. 9 (January 2018)
21/39
2.4.1
Line loop
In the line-loop configuration (see Figure 12), the output of the transmission transformer is
connected to the input of the reception transformer. At the same time the transmission and
reception lines are interconnected in order to establish a loop in the remote modem.
Figure 12 Line loop carried out in local modem
In order to carry out the line loop, microswitch 6 should be in ON position. The LEDs TEST
and LINE LOOP on the front plate of the terminal light up to indicate this situation, both
being amber.
2.4.2
Data loop
As can be seen in Figure 13, a double loop is carried out in the local loop; on the one hand,
the TD and RD signals are looped, which checks the RS-232C interface (connection
between DTE and modem) and, on the other, the signal coming from the remote modem,
once demodulated, is modulated again and is transmitted towards the line. Given that in this
situation the transmitter must always be ready for transmission, the RTS signal is internally
maintained as active. The TD and RD LEDs of the local modem remain associated to it and
not to the DTE.
Figure 13 Data loop carried out in local modem