USB-4COMi-M/USB-4COMi-SI-M Hardware Settings and Pinouts

Outside the unit, there are four 4-pin DIP switches used to select the mode of operation. You can switch to RS-422 mode or RS-485 mode as per the requirements of your application. After setting the operation mode and connecting power supply to the adapter, you can then plug the adapter to a USB port to start driver installation.

 

RS-422 & RS-485 Mode Configuration

 

Operation Mode S1 S2 S3 S4
RS-422 4 wire with handshaking ON ON OFF OFF
RS-485 Full duplex (4 wire) ON OFF OFF OFF
Half duplex (2 wire) with echo OFF OFF OFF ON*
Half duplex (2 wire) without echo OFF OFF ON ON*

 

*Note: In the most common situation, a 120Ω termination resistor of TxD (S4 is ON) is required in a RS-485 half-duplex configuration. Otherwise it is rarely used.

 

Termination & Bias Resistor Configuration

Inside the unit, there are four 6 × 2 (8 pin) header blocks which are jumpered to enable Rx, CTS 120Ω termination resistors and Rx, Tx 750Ω biasing resistors.

You will need to open up the case to set the jumper settings as per the requirements of your application.

 

Jumper Function
1-2 Pull-up Tx+ to VCC by 750Ω bias resistor. This jumper should be populated for pull-up Tx+.
3-4 Pull-down Tx- to GND by 750Ω bias resistor. This jumper should be populated for pull-down Tx-.
5-6 Rx+/- termination of 120Ω. This jumper should always be populated for RS-422 and RS-485 full duplex mode.
7-8 Pull-up Rx+ to VCC by 750Ω bias resistor. This jumper should be populated for pull-up Rx+.
9-10 Pull-down Rx- to GND by 750Ω bias resistor. This jumper should be populated for pull-down Rx-.
11-12 CTS termination of 120Ω. This jumper should always be populated for RS-422 mode.

 

Note: Sometimes, when operating in RS-422 or RS-485, it is necessary to configure termination and biasing of the data transmission lines. Generally this must be done in the cabling, since this depends on the installation of connections. Before applying the option, check your cable specification for proper impedance matching.

Biasing of data lines must only occur at a single point anywhere in the cabling. USB-4COMi-M and USB-4COMi-SI-M provide biasing for ease of installation. Please be sure to disable this inside the unit, if your cabling already provides biasing.

Termination must not be installed in the middle of the cable. It is only permitted at both ends. Since a computer controlled serial port is almost always at one end of the cable, termination is enabled by default. Rx-Termination is inside the box, because you hardly ever need to change it. Tx-Termination is used in half-duplex modes. In this situation data is sent and received via Tx+/- lines. Therefore Tx-Termination is done via a DIP switch (see S4 above).

 

RS-422/485 DB9 Male Connector Pinouts

 

 

RS-422 DB9 Male Connector Pinouts

 

PIN SIGNAL
1 TxD- (A)
2 TxD+ (B)
3 RxD+ (B)
4 RxD- (A)
5 GND
6 RTS- (A)
7 RTS+ (B)
8 CTS+ (B)
9 CTS- (A)

 

RS-485 4-Wire (Full duplex) DB9 Male Connector Pinouts

 

PIN SIGNAL
1 TxD- (A)
2 TxD+ (B)
3 RxD+ (B)
4 RxD- (A)
5 GND

 

RS-485 2-Wire (Half duplex) DB9 Male Connector Pinouts

 

PIN SIGNAL
1 Data- (A)
2 Data+ (B)
5 GND

 

RS-422/485 Signal Wiring

RS-422

Point-to-Point 4 Wire Full Duplex

 

 

RS-422 with Handshaking

 

 

RS-485

Point-to-Point 4 Wire Full Duplex

 

 

Multidrop RS-485 2-Wire Half-duplex