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Connection
TTY passive
b) MA 21 passive/host active:
Host
Ground (shield)
Figure 5.3: Passive connection of the MA 21120 to a TTY host computer
Hints for connecting the TTY interface:
• The active subscriber is the one which supplies the current (20 mA).
• Switching between active/passive on the host interface card is carried out using two
jumper pairs, independent for transmit (Tx) and for receive (Rx).
• The jumpers for active/passive switching must always be changed in pairs (upper and
lower jumpers in the same position). Thus the current source and GND are switched
internally at the MA 21 host interface module.
• Mixed operation is possible (transmit active/receive passive or vice versa).
• When switching between active and passive operation or vice versa, the pin order of
the connection cable is changed (pin assignment).
22
+20mA
R x+
R x -
Jumper
G N D
+20mA
T x+
T x -
Jumper
G N D
up to 1000 m
Shield
MA 21
Host interface module
TTY
TX+
1
TX-
2
RX+ 3
RX-
4
-
5
G
N D 6
Jumper position
passive
Leuze electronic
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