Hardware Setting & Mode Configuration
Outside the unit, there is one 4-pin DIP switch which is set to select the mode of
operation. You will need to set the switch settings to RS-232 mode, or RS-422, or RS-485
mode as per the requirements of your application.
The Mode Block Configuration Settings are listed as follows:
SW (External DIP Switch) for Mode Setting
Operation Mode S1 S2 S3 S4
RS-232 Standard RS-232 Mode OFF ON ON ON
RS-422 4 wire with Handshaking ON ON ON ON
RS-485 Full Duplex (4 wire) ON OFF ON ON
Half Duplex (2 wire) ON OFF OFF ON
- with Echo
Half Duplex (2 wire) ON OFF OFF OFF
- without Echo
JP1 for Termination and Biasing Option Configuration
Inside the unit, there is one 2 x 7 (14 pin) header blocks which are jumpered to enable Tx,
Rx, CTS 120 Ohm termination resistors and Tx, Rx 750 Ohm BIASing resistor.
You will need to open up the metal case and set the jumper setting for RS-422 mode or
RS-485 mode as per the requirements of your application.
Settings are listed as follows:
Jumper Function
1-2 Tx Termination of 120 Ohm.
This jumper should always be populated for RS-485 mode.
3-4 Pull-up Tx+ to VCC by 750 Ohm Bias resistor.
This jumper should be populated for pull-up Tx+.
5-6 Pull-down Tx- to GND by 750 Ohm Bias resistor.
This jumper should be populated for pull-down Tx- .
7-8 Rx Termination of 120 Ohm.
This jumper should always be populated for RS-422 mode.
9-10 Pull-up Rx+ to VCC by 750 Ohm Bias resistor.
This jumper should be populated for pull-up Rx+
11-12 Pull-down Rx- to GND by 750 Ohm Bias resistor.
This jumper should be populated for pull-down Rx- .
13-14 CTS Termination of 120 Ohm.
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.
JP2 : Enable the +5V 150mA Power for External Device
The USB-COMi-M provides a unique feature of supplying power output of 5V/150mA
through Pin-5 of terminal block to the serial device requiring power. By default, this
feature is disabled. To enable the power, you need to open the metal case and set the
jumper (JP2) to the position of “ON”.
Jumper Function
ON Enable the Terminal Block Pin-5 to support a 5V 150mA power for
external device requiring power
OFF Disable the 5V 150mA power (Default)
RS-232/422/485 Pin-outs & Signal Wiring
RS-232 Signal Pin-outs of DB-9 Male (CN2)
Pin 1 DCD
Pin 2 RxD
Pin 3 TxD
Pin 4 DTR
Pin 5 GND
Pin 6 DSR
Pin 7 RTS
Pin 8 CTS
Pin 9 RI
RS-232 Signal Pin-outs of Terminal Block (TB1)
Pin 1 DCD
Pin 2 RxD
Pin 3 TxD
Pin 4 DTR
Pin 5 +5V
Pin 6 GND
RS-422 Signal Pin-outs of DB-9 Male (CN2)
Pin 1 Tx- (A)
Pin 2 Tx+(B)
Pin 3 Rx+(B)
Pin 4 Rx- (A)
Pin 5 GND
Pin 6 RTS- (A)
Pin 7 RTS+(B)
Pin 8 CTS+(B)
Pin 9 CTS- (A)
RS-422 Signal Pin-outs of Terminal Block (TB1)
Pin 1 Tx- (A)
Pin 2 Tx+(B)
Pin 3 Rx+(B)
Pin 4 Rx-(A)
Pin 5 +5V
Pin 6 GND
RS-422 Signal Wiring
Point-to-Point 4 Wire Full Duplex
RS-422 with Handshaking
RS-485 4-Wire (Full duplex) Signal Pin-outs of DB-9 Male (CN2)
Pin 1 Tx- (A)
Pin 2 Tx+(B)
Pin 3 Rx+(B)
Pin 4 Rx-(A)
Pin 5 GND
RS-485 4-Wire (Full duplex) Signal Pin-outs of Terminal Block (TB1)
Pin 1 Tx- (A)
Pin 2 Tx+(B)
Pin 3 Rx+(B)
Pin 4 Rx-(A)
Pin 5 +5V
Pin 6 GND
RS-485 2-Wire (Half duplex) Signal Pin-outs of DB-9 Male (CN2)
Pin 1 Data- (A)
Pin 2 Data+(B)
Pin 5 GND
RS-485 2-Wire (Half duplex) Signal Pin-outs of Terminal Block (TB1)
Pin 1 Data- (A)
Pin 2 Data+(B)
Pin 5 +5V
Pin 6 GND
RS-485 Signal Wiring
Point-to-Point 4 Wire Full Duplex
Multidrop RS-485 2-Wire Half-duplex
