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Industrial Port-Powered RS232 to RS485 Converter

Model: CVT-485-1

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The CVT-485-1 is a compact, rugged, industrial-grade, port-powered, bi-directional RS232 to RS485 converter, which can be used to convert any standard unbalanced RS-232C port into a two-wire half-duplex balanced RS485 port and vice versa.

This industrial-grade RS232 to RS485 converter operates within a wide temperature range (-40F to 185F / -40C to 85C), features 600W surge protection and 15kV static protection, and comes with a built-in 120 Ohm terminator for system reliability and easy installation. The unit is powered from the RS232 data line; it also supports data direction auto-turnaround, which automatically enables the RS485 transceiver when data is present on the RS232 side. Therefore, it requires no external power, software drivers or flow control, making the unit a rugged, highly reliable, and truly plug-and-play device.

Declaration of Conformity | RS232 to RS485 Converter data sheet


- Converts RS232 to 2-wire RS485 and vice versa.
- 300 to 115.2K Baud operation (auto-sensing & self-adjusting).
- Industrial grade with wide temperature range (-40F to 185F / -40C to 85C), surge (600W) and static protection (15kV).
- Port-powered, no external power or RTS, DTR required.
- Accepts external 5VDC regulated power if the port-power is insufficient.
- Plug and play (hot-pluggable, data format auto-sensing & self-adjusting).
- Data direction auto-turnaround, no flow control is required.
- Built-in surge protection, static protection and circuit protection.
- Built-in 120Ω end-of-line terminator for system reliability and easy installation.
- Surface Mount Technology manufactured to ISO-9001 standards.
- CE certified: strictly certified by world-class lab TUV.
- 5-year manufacturer's warranty.

120 Ohm End-of-Line Terminator (Built-in)

Self-explanatory, the 120 Ohm end-of-line terminator is to be connected at the end of the RS485/RS422 transmission line. This is important for building a reliable RS485/RS422 system, not only because of impedance matching, but also for the reduction of signal reflections and noise problems.

Note: The 120 Ohm end-of-line terminator adds heavy DC loading to a system and, therefore, it should be connected only when the RS485/RS422's distance is over 660ft (200m).


RS232 to RS485 converter / View 2 RS232 to RS485 converter / View 3 RS232 to RS485 converter / View 1


Part Number: CVT-485-1
Compatibility: EIA/TIA RS-232C standard and RS-485 standard
Power Source: Port power from RS232 data line
Current Consumption: Less than 10mA
Baud Rates: 300 to 115,200bps (Auto-sensing & Self-adjusting)
Distance: Depending on power from RS232 port, will transmit up to 4000ft (1.2km) at 19,200bps
Connector: RS232 Side: DB-9 Female; RS485 Side: DB-9 Male; Termination Board: DB-9 Female and a 4-Way Terminal Block
Maximum number of drops: 128
End of Line Terminator: 120Ω (Built-in)
Surge protection: 600W
Static protection (ESD): Up to 15KV
Dimensions (H x W x D): 0.63 x 1.3 x 3.4 in (16 x 32 x 86 mm)
Weight: 1.27 oz (36 g)
Operating Temperature: -40F to 185F (-40C to 85C)
Operating Humidity: Up to 90% RH (no condensation)


RS232 Side

Pin 1 4 6 7 8 2 3 5
Function Tied Tied TX RX GND
RS232 RS485 converter - RS232 DB9 Female PinoutsNote: Some software requires handshake line acknowledgements. To satisfy the requirements, our converter's handshake lines are tied together (DCD, DTR, and DSR tied together, and RTS and CTS tied together). Therefore, you don't have to modify your existing software.

DB-9 Female (view from front)

RS485 Side

Pin 1 3 5 9 6 7
Terminal Block A+ B- GND +5V Jumper (120)
Function RS485+ RS485- GND +5V measurement Terminate/remove Jumper 120 to turn ON/OFF the 120Ω end-of-line terminator.

RS232 to RS485 converter - DB9 and Terminal Block pinoutsNote: The CVT-485-1 comes with a 4-way terminal block for easy wire connections. However, you may choose not to use the terminal block provided and simply follow the above table for pin assignments. DB-9 Male (view from front) / Terminal Block


RS232 to RS485 converter - RS485 bus 120 Ohm end-of-line terminator Jumper settings

IMPORTANT: Turn ON Jumper 120 (120 Ohm End-Of-Line Terminator) at both ends of the RS-485 bus.


RS232 RS485 Converter - Connection
Figure 1: Master-Slave Multi-Drop Connections
RS232 RS485 Converter - Diagram
Figure 2: Extending Half-Duplex RS232 Distance (Data Only)


1) Port power measurement
RS232 to RS485 converter - port power measurement
Measure pin +5V and GND with a voltmeter, and be sure that it is around +5VDC (when RS232 port is connected).
2) Loopback Test
RS232 to RS485 converter - loopback test
  • Connect two numbers of CVT-485-1 to your PCs COM ports and connect A+ to A+, B- to B- on the RS485 terminal blocks (as shown above).
  • Run two instances of the 232Analyzer FREE version software on your computer.
  • Select "ASCII" for both the Send and Receive data formats. Then send command and/or string such as "CommFront" from one COM port. You should receive an echo of the command/string sent ("CommFront") on the other COM port. By performing a simple loopback test like this, you can test both the transmitter and receiver of the converter. This is very helpful when you are in doubt about the performance of your converter.
RS232 RS485 Converter - Loopback test by using CommFront 232Anlayzer software
Screenshot 1: Send commands from 1st instance of the 232Analyzer software.
RS232 to RS485 Converter - Loopback test by using CommFront 232Analyzer software
Screenshot 2: Receive commands from 2nd instance of the 232Analyzer software.

232Analyzer is an advanced RS232 Serial Protocol Analyzer software that allows you to control, monitor and analyze serial port (RS232 / RS485 / RS422 / TTL, etc.) activities. Not just the data, it also allows you to monitor or change RS-232's line states: RTS, CTS, DTR, DSR, DCD, and RI. The FREE version (no time limitation) can be downloaded from here.

  • Model: CVT-485-1
  • Shipping Weight: 0.1lbs
  • Manufactured by: CommFront

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