PSM-ME-RS232/TTY-P
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6 Application examples
Figure 1 Application example
Interface adaptation between RS-232 and TTY standard
– TTY dedicated line for visualization and process data
capture
– Programming/parameterization connection
TTY basics
The TTY current loop interface is used, for example,in
programmable logic controllers (PLCs), on displays, and
printers. Separate cable pairs are needed for the transmit
data and the receive data.
Data is transmitted in full duplex mode using a software
handshake. No provision is made for control cables.
A loop current of 20mA represents the “Logic1” state. If the
circuit is interrupted, this is interpreted as “Logic0”. Each
loop requires a current source which is coupled to either the
transmitting or the receiving side. The current sourcing side
is described as active and the passive side is always
opposite it.
There are three possible interface configurations:
– Fully active TTY interface with current sources in both
the transmitter and receiver branch
– Passive TTY interface without the relevant constant
current sources
– Semi-active TTY interface with source currents only on
the transmitter side (TD). The receiver (RD) is passive.
In order to establish a TTY transmission path, the type of
interface must be known. There are two options for a
connection path:
– A fully active device and a passive device
– Two semi-active devices
RS-232
(V.24)
RS-232
(V.24)
15 m
TTY
TTY
1000 m
Interface adaptation
Te c h ni cal d at a
Standards DIN66258-1, DIN66348-1
Transmission speed 19.2 kbps
Transmission length 1000meter
Procedure Current loop
Principle Full duplex, point-to-point
