Tty Interface 20 Ma - Tally T2265 SprintPro Maintenance Manual

Functional Description
3.3.3.3

TTY Interface 20 mA

The interface signals generated in the microprocessor and in the application's
specified IC are connected to the interface optocoupler IC1 (Type SFH 618).
This IC switch the TTL-signals on the microprocessor side to the level of the current
loop without any galvanical contact.
Received signals on the Rx loop should be changed by the optocoupler IC2 from
current loop level down to TTL-level (Type HCPL 4200).
DIP switches (S1, S2) are provided to select Active, Passive, (TX, RX).
L4 BLM31
C6 33N
63V M
62130
B5
Electronic Functions
X2
26
25
24
23
22
21
20
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18
17
16
15
14
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12
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8
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4
3
2
1
27
CHASSIS
+TXLOOP
-TXLOOP
+RXLOOP
-RXLOOP
GND*
CHASSIS
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