Westermo MA-29 - Manual (Page 12)

12 6029-2002
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The 20 mA current loop interface, or TTY as it is sometimes known, is a popular
industrial communications standard. The system relies on a current generator running on
both the transmit and receive circuits. On each circuit it is important to have only one
current generator supplying current into that circuit. For this reason the MA-29 can
have it’s current generators set to be either active or passive. It is important to check
the state of all attached equipment to ensure correct setting on the MA-29.
The RS-232 interface is configured as DCE (Data Communication Equipment).
Most printers, PC’s and terminals are set as DTE (Data Terminal Equipment).
Some recomendation of cable configurations are given below.
If any problems do occur on set up of the MA-29, the LED’s will be helpful.
• RD: Data received on line interface.
• TD: Data received on RS-232 interface.
• +12V, –12V: Positive and negative power supply respectivly.
A good way to check the MA-29 is to carry out a loop back test. Ensure that either the
transmitter or receiver are set to active, but not both active or passive. Connect T+ to
R+ and T– to R–. Connect the RS-232 port to a terminal. When keys are pressed on
the terminal you should receive the echo on screen. The TD & RD lights will both flick-
er simultaneously as you press the keys.
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DTE MA-29 DCE MA-29 9-pol PC MA-29