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6.2 Half Duplex Operation

The DSP-200/300’s ports may be configured for either full duplex or half duplex operation. By

default, the RS-422/485 ports are configured for full duplex operation with the RS-422/485

output drivers always enabled.

In half duplex mode, the RS-422/485 transmitter may be enabled and disabled via the RTS

(request to send) or DTR (data terminal ready) signals. Both RTS and DTR are controlled

through the Modem Control Register of the 16750.

RS-422/485

Driver

RS-422/485

Driver

Data Out

Aux Out

Active Low

Output Enable

3 Options:

Half Duplex

16C550

-RTS

-DTR

NOTE:

One of these three options must be selected via

software configuration. Full duplex operation is

the default mode.

Full Duplex

MUX

Figure 11. RS-422/485 Driver Enable Options

If RTS is selected as the signal to enable the output drivers, setting 'bit 1' of the Modem Control

Similarly, if DTR is chosen as the signal to enable the output drivers setting 'bit 0' of the Modem

Control Register (to logic '1') will enable the output drivers and clearing 'bit 0' of the Modem

Control Register (to logic '0') will force the outputs into a high impedance state.

Hardware Information 6-3

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Quatech DSP-200/300 Bedienungsanleitung Seite 45