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PCI VelocityRS232/422/485
Additional RS422/485 Operation
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 5-5. RS485 Jumpers, Full Duplex.
Both jumpers left unconnected (not shorted).
Figure 5-6. RS485 Full Duplex.
Note: The receiver end of MAIN line terminated in characteristic
impedance, stubs off the main not terminated.
Optional Grounding Arrangements.
Proper operation of the cable circuit, according to TIA EIA: 485 A
(1995) requires that the cable ground shield is not connected
directly to the equipment ground shield. A current limiting resistor
should be used in series with the shield to avoid possible large
current flow due to differences in ground potential. Any one of the
methods shown in Figure 5-7, below can do this.
Chapter 5 Page 78
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