Self powered full duplex RS232C to RS422 converter

I need a self powered full duplex RS232C to RS422 converter to transfer program to and from a Brazilian brand WEG PLC. To do so the mentioned interface is necessary.

The only pins on RS232C side will use are DB9 connector 2, 3 and 5.

Regards,

Fernando - Call sign PU2PLL - Brazil

Hi,
By self powering if you mean taking the power from the RS232 TX signal, I would advise you against it as it would limit the current for the RS422 driver. Proper method is to use a Max232 like device followed by a Max 491 like RS422 IC with a local 5V supply for the interface, which will work under all conditions, otherwise the Murhy's ghost will show up its ugly head off and on.

Regards,
Laktronics

I would agree with laktronics, do not attempt this with only a three pin serial port. There are self powered converters on the market and they work fine. However, they rely on using the optional RS232 control pins as power sources. Specifically, RTS and DTR. To use these converters, the PC software must set RTS and DTR to the appropriate level and keep them there. If the OS or some other software accesses that serial port and changes these control lines, the converter becomes unpowered and communication fails.

A simple and more bullet proof solution is to get your power elsewhere. The USB port has a dedicated +5V power source for external devices. I would suggest buying a USB to RS232 converter. Open it up and connect into the +5V supply to get power for your MAX232 and your RS422 transceiver. Then everyone is happy. The ICs get a dedicated power source that is stable and the OS sees a serial port with all the proper mappings and no special control pin setups.

----- Steve

to make it "full-duplex" it will need small modifications but once you see this circuit and understand how it works you should be able to do it ..

all what you can do is just to try it ..

rgds,
ianp