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3.3 RS-422/485 Interface Specification
3.3.3 Precautions when transferring data using RS-422/485 line
3
SPECIFICATIONS
3.3.3 Precautions when transferring data using RS-422/485 line
Note the following points when performing data communication with a target device
through the RS-422/485 interface of QJ71MB91.
For the target device side, pay attention to the following when sending/receiving data.
(1) Preventive measures against faulty data reception on the target device
side
If the target device receives error data, install a pull-up or pull-down resistor to the
target device as shown below.
Installing a pull-up or pull-down resistor (resistance value: approx. 4.7 k , 1/4 W) can
prevent the reception of error data.
POINT
Error data will not be received if a pull-up or pull-down resistor is connected on the
target device side.
Remark
The case where any pull-up or pull-down resistor is not connected on the target
device is described below.
When any station is not performing transmission, the transmission line is in a high
impedance status and the line status is not stable due to noises, and the target
device may receive error data.
In such a case, parity or framing error may have occurred. Skip data reading for
error data.
Figure 3.3 Preventive measures against faulty data reception
+
-
Receive data
Target
device
Terminating
resistor
RDA
RDB
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