VIPA SSM-BG41, Manual

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Functional description and allocation of terminal pins Manual BG41/BG42/BG43
3-4 Rev. 99/49
3.2 Functional description and allocation of terminal pins
3.2.1 20mA current loop-modul (MD25)
3.2.1.1 General
The RS232C interface can no longer be sufficiently relied upon in an environment where high
interference levels are expected. The 20mA current loop interface was therefore developed. With
this interface a logical "1" is implemented through a current of 20mA and a "0" through 0mA. The
respective currents are generated in an active suscriber and are led through a loop back to the
sender. Only two circuit pairs are therefore required.
Point-to-point or bus connections can be realised with the 20mA current loop module. The module
contains two line current loops for transmission and reception. In bus operations the module in a
voltage-free state connects all loops, in order to prevent the entire system from being impaired.
In its delivery state the interface module 20mA current loop is set to the internal voltage supply
through the back plane bus. If the external voltage supply is switched to the 20mA current source,
the jumpers X3 and X5 must be replugged.
Transmit Data
(red LED)
Receive Data
(red LED)
30-pole Plug
26-pole Plug
Jumpers for 24 V Current Supply
(Internally through back plane bus or externally)
LEDs:
Continous Light : No Data Transmission
(Sleep Mode)
Flickering Light : Data Transmission in Progress
X3
X5
M24
INT
EXT
P24
INT
EXT
Fig. 3-1: Structure of the 20mA current loop-moduls