Acces I/O products PCI-COM485/4, Руководство пользователя

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Chapter 3: Option Selection
To help you locate the jumpers described in this section, refer to the Option Selection Map at the end of
this section. Operation of the serial communications section is determined by jumper installation as
described in the following paragraphs.
Terminations
A transmission line should be terminated at the receiving end in its characteristic impedance. Installing
a jumper at the locations labeled LDxO applies a 120
Ω load across the transmit/receive
input/output for RS485 operation.
120
Tx+/Rx+
TX-/Rx-
LDxO
Figure 3-1:
Simplified Termination Schematic
In RS485 operations where there are multiple terminals, only the RS485 ports at each end of the
network should have terminating impedance as described above. To so terminate the COM A port,
place a jumper at the location labeled LDAO. To terminate the COM B, COM C, and COM D ports,
place jumpers at locations labeled LDBO, LDCO, and LDDO respectively.
Also, for RS485 operation, there must be a bias on the RX+ and RX- lines. If the card is not to provide
that bias, contact the factory technical support.
Data Cable Wiring
Signal Pin Connection
TX+
and RX+ 2
TX- and RX- 3
Ground 5
Baud Rate Ranges
The jumpers labeled CLK X1 and CLK X4 select the baud rates in either of two ranges. When in the
"X1" position, the baud rate range is up to 115,200 baud. When in the CLK X4 position, the baud rate
range is up to 460,800 baud.
Note
Refer to Table 5-1, Baud Rate Divisor Table on page 5-1 of the manual.