RS232/RS485 interface
Two serial interfaces are wired on the D-Sub socket: one with RS232 and one with RS485 physics. Both interfaces have the same potential and are electrically isolated from the CPU. The interfaces can be used simultaneously and work independently of each other.
Observe the PIN assignment of the D-Sub socket when assembling cables for wiring. The ZB3180 connector with two cable outlets can be used for wiring (see: D-sub connector ZB3180).
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. A termination resistor can lead to an improved transmission level in cases where long lines, a high line resistance, a large number of RS485 devices and/or high baud rates are used. RS485 is implemented in different ways, and it is not necessarily clear whether a termination resistor improves or impairs the result.
Our recommendation is to use an active termination resistor (PIN4 - 390 Ohm, PIN1 - 220 Ohm, PIN6 - 390 Ohm, PIN5/9). PIN4 is assigned 5 VDC and PIN5/9 GND for the active termination resistor (RS485). PIN4 should only be used for the termination resistor. Do not operate any other electrical components on PIN4, otherwise the CX8180 may be destroyed.