Full duplex mode uses 4 wires to transmit and receive data. Half duplex mode uses 2 wires to transmit and receive data and can only transmit or receive at any one time. To set an RS422/485 device into half duplex mode both the hardware and the drivers must be set correctly. Hardware To set half duplex for a PCI or ISA card, connect the supplied jumpers across the header pins on the PCB so that TX+RX+ are shorted together and TX-RX- are shorted together. For a PCMCIA card, there are no headers on the card itself so the short must be created within the cable being used to connect the PCMCIA card to the other device. This is performed by shorting pins 1&6 and 2&7 using two pieces of wire. Drivers To set half duplex for PCI, ISA or PCMCIA card, for Windows 98, 2000, XP onwards access Device Manager and double click on the card’s entry to access the Property pages. For Windows NT go to the Serial Solutions Control Panel applet. Choose to change the card’s mode to Half Duplex mode. Software To set half duplex access Device Manager and double click on the card’s entry to access the Property pages.

 


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