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RS422/485 Information
PCI VELOCITY / OPTO ISO RS422/485
at any one time. Each RS485 device recognizes commands and data
addressed to it, it only talks when the PC commands it to do so.
When the RS485 device receives the command to talk from the PC,
it gates its TXD drivers on, sends the data down the device TXD
channel, and disables its TXD drivers. The other RS485 devices
remain in the receive only mode when they are not being addressed,
they do not transmit any data at all. Figure 4-5 gives the jumper
settings for the serial card in the RS485 Full Duplex mode.
Figure 4-5. RS485 Jumpers, Full Duplex.
Both jumpers left unconnected (not shorted).
Figure 4-6. RS485 Full Duplex.
Note: The receiver end of MAIN line terminated in characteristic
impedance, stubs off the main not terminated.
Chapter 4 Page 48
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