Modicon Products
      Square D Products
Download Area
Price List
Application Notes
RS-422/485 <> RS-232 converter

The DDC2I is a DIN rail mounted optically isolated RS-232 to RS-422/485 converter. It is especially designed for use with Modicon® PLCs and Niobrara communication modules equipped with RJ-45 RS-232 ports.
RS-232 port:

The DDC2I's RS-232 port has an RJ-45 connector designed to use straight through cabling from the RJ-45 RS-232 port of a Modicon Micro PLC, TSX Momentum™ PLC, TSX Compact PLC, NOM 252 or NR&D QUCM or CUCM. A variety of serial cables are available from Niobrara to allow the DDC2I to be used with other standard RS-232 ports. The DDC2I comes with an MM0 cable but any other MM cable may be substituted when ordering.

RS-422/485 port:

The DDC2I has two RS-422/485 connectors to increase flexibility. A DB9 connector has the standard SY/MAX® pinout for use with Square D SY/MAX devices and standard SY/MAX cabling. The other connector is a removable screw terminal that is wired in parallel to the DB9 connector for use with POWERLOGIC® equipment or other RS-422/485 devices.

The DDC2I supports 4-wire RS-422, 4-wire RS-485 multidrop or 2-wire RS-485 multidrop networks. It contains terminating and biasing resistors that can be disabled and can run in Master or Slave mode. Multidrop operation is controlled by the RS-232 RTS pin.


The DDC2I enables the user to:

  • Build a serial network of Modicon PLCs Use a Modicon PLC as the master of a Modbus® RS-485 multidrop network.
  • Use a Niobrara QUCM-S to communicate with a network of RS-485 devices.
  • Run RS-232 signals further than 50 feet.

Common RS-422/485 Masters
Common RS-232 Masters
Common RS-422/485 Slaves
Common RS-232 Slaves


Many Modicon-style RJ-45 RS-232 ports, such as those of the Modicon Micro PLC, TSX Compact PLC and the NR&D QUCM-S supply 5VDC power to the DDC2I. For installations using other equipment the DDC2I must be powered by 9 to 24 VDC through a removable screw terminal power connection. A Niobrara TR92 wall-mount transformer is provided with the unit for this purpose. If suitable power is already available, the DDC2I may be obtained without the transformer at a reduced cost (order part number DDC2I-NT). Consult the current price list for pricing information.

The DDC2I comes with both a 5-position removable screw terminal RS-422/485 connector and a 2-position removable screw terminal power connector. The DDC2I has a one year warranty; see Niobrara's Standard Terms and Conditions of Sale for details.


Dimensions: 2.8" wide x 3.7" high x 2.3" deep (71 x 94 x 59mm); approximately 4 oz. (114g) net. All connectors and indicators front mounted.

Power Requirements: From Modicon Micro PLC, Modicon TSX Compact PLC, or QUCM-S: 5 VDC 250 mA max; from external power supply: 9-24 VDC, 1.6 W max.

Operating Conditions: 0 to 50 degrees C operating temperature; -40 to 80 degrees C storage. Humidity up to 90% noncondensing. Pressure altitude -200 to +10,000 feet MSL.

RS-232 Port: 8-pin RJ-45 connector. Data transfer rates up to 115.2 Kbaud

RS-422/485 Port: SY/MAX compatible DB9 female connector with slide-lock posts or 5-position Phoenix Combicon connector. 2-wire and 4-wire compatible. Terminator impedance: 120 ohms. RS-422 bias level: 6 mA (+/- 1mA).

Configuration: 6-position DIP switch sets RS-422/RS-485 for 2-wire/4-wire mode; Master/Slave; Terminating Resistor on/off; Bias Network on/off.

Isolation: 1500 V rms Indicators Green LEDs for Power and TX Enabled; Amber LEDs for TX and RX. Four total indicators.


The DDC2I is available as:
DDC2IRS-422/485 <> RS-232 converter with an MM0 cable.
DDC2I-3RS-422/485 <> RS-232 converter with an MM3 cable for connecting to a Modicon 9-pin RS-232 port.
DDC2I-5RS-422/485 <> RS-232 converter with an MM5 cable for connecting to a standard PC 9-pin RS-232 port.
DDC2I-6RS-422/485 <> RS-232 converter with an MM6 cable for connecting to a standard Modem 25-pin RS-232 port.
DDC2I-15RS-422/485 <> RS-232 converter with an MM15 cable for connecting to an MUCM 5-position screw terminal RS-232 port.

DDC2I Accessories:
DC1 RS-422 cable for connecting to a SY/MAX PLC port. Order a DC1 with a DDC2I-5 as an optically isolated replacement for an SC902 or Square D ICM-200 converter.
TR95-ST Replacement 12VDC wall mount transformer for powering a DDC2I.
PC2 Replacement Orange 2-position power connector.
NC5 Replacement Green 5-position RS-485 connector.

Effective 01 May 1999 - Specifications subject to change without notice.