Communication solutions for power utilities
1U SHELF TYPE MAS-2
WITH ASYNCHRONOUS PROGRAMMABLE MODEM MAFP - Rev. 9 (January 2018)
20/39
The receiver also has a carrier-detection circuit that controls the interface CD signal. When
the level of the received signal falls below the established signal, the CD output, which is
positive, changes to negative and the corresponding LED goes out. This condition causes
the receiver to block and general alarm relay to activate.
For half-duplex operation, a selection that is carried out by means of microswitch 1 on the
front plate, the receiver is blocked when the RTS signal activates, that is to say, during the
transmission of data.
2.3
GENERAL ALARM
The MAFP modem constantly supervises the level of the received signal and, should this be
14 dB below the nominal level, the general alarm is activated. It must be taken into account
that there is an hysteresis of 3 dB.
The general alarm is indicated by the STATUS LED lit permanently in red, and externally by
means of relay. This relay, however, can be disabled by means of the internal microswitch
MI2, as explained in chapter 4,
In normal operation the alarm relay is energized, so that, a disappearance of the power
supply provokes the fallen of the relay, and so, the general alarm.
2.4
TEST DEVICES
The test devices are used to facilitate maintenance, commissioning and fault-finding
operations. They are based on the action of the CONFIGURATION microswitches on the
front plate of the module.
It must be borne in mind that if the modem is working in V.23 mode of the ITU-T, it is not
possible to carry out any kind of loop as the transmission and reception speeds do not
coincide.
When a loop or the sending of tests signals is carried out, the DSR signal is disabled.