Mounting and wiring
3.2.3
RS232/RS485
D-Sub connector
Two serial interfaces are wired on the D-sub connector of the CX8080. These two interfaces are on same
potential and are electrically isolated towards the CPU. Both interfaces can be used simultaneously and work
independent of each other.
Pin assignment X101 of the CX8080
PIN
Meaning
Description
Signal
1
RS485
(+)
A
2
RxD (RS232)
Signal in
Receive Data
3
TxD (RS232)
Signal out
Transmit Data
4
+ 5 V
+
Vcc
5
GND
Ground
Ground
6
RS485
(-)
B
7
RTS (RS232)
Signal out
Request to Send
8
CTS (RS232)
Signal in
Clear to Send
9
GND
Ground
Ground
Termination resistor
Usually no termination resistors are required for low baud rates. In situations with long line lengths, high line
resistance, a large number of RS485 devices or high baud rates, a terminating resistor can result in
improved signal level for the transfer. Unfortunately, there are a number of different RS485 implementations,
so that it is difficult to determine in advance whether a terminating resistor may improve the result or perhaps
even make it worse. It is advisable to use an active terminating resistor (PIN4 - 390 ohm - PIN1 - 220 ohm -
PIN6 - 390 ohm PIN5/9).
PIN44 is assigned 5 V
DC
and PIN5/9 GND for the active terminating resistor (RS485). These must never be
misused for other functions, as this can lead to destruction of the device.
CX8080
19
Version: 1.0.0
