RS485 to RS232 converter

RS232 needs some loopbacks: DTR-DSR-DCD, CTS-RTS

checkout the data sheet on Maxim, Max3161, or Max3162. Ya missing a few connections as well http://www.ortodoxism.ro/datasheets/maxim/MAX3160-MAX3162.pdf

Both proper wiring and proper termination resistors are important.

If you intend to use very long wires, try making it work over shorter wires first.

Also take a better look at the temperature scanner documentation. TD+, TD-, RD+, RD- would make more sense.

Modbus RTU protocol needs that you perform some configurations, slave ID and regular serial parameters.

By proprietary software, du you mean it is purchased (rSCADA) or that you developped it?

You may have to jumper TD+ to RD+ and TD- to RD- on the scanner since it appears that the converter is a half-duplex system. Or if they aren't label as such, then connect D+ to D+ and D- to D-. Then connect D+ on the scanner to D+ on the converter and D- to D-. If that doesn't work, flip them, D+ to D- and D- to D+.

Read the documentation carefully on the converter. Sometimes all nine connections of the RS-232 link is required and the exact connections can vary. (Not necessarily a one-to one cable, could be null modem, and other connections can be non-standard as well, speaking from my own frustrated experiences eventually remedied by reading the instructions ) The 15 pin D-sub is somewhat unusual for a serial port as it usually is a 9 pin D-sub (Standard density, Shell size 1) or the 25 pin D-sub (Standard density, Shell size 3).

Make sure the PC software is configure to look at COM1 and all the parameters are set per the instructions, parity, baud rate, etc. Good luck in your quest !!

1. Post 4 was correct. Check your temperature scanner/converter documentation for the phrase 2-wire and 4-wire setup. I bet if you check the temperature scanner carefully you will find a T or XMT above one set of D+,D- terminals. You may have to get someone who can read braille if the device is old.

2. Post 1 was correct.Check your PC/converter documentation for the phrase software/hardware handshaking. Usually there will be a jumper setup on the converter. If not then you may have to do some jumpering on the PC end of the cable.

3. Check the cable/doc for the converter (if the cable didn't come with the converter), to determine what type of DTE-DCE setup is required on the cable.

4. There are a lot of good sites (some mentioned above) for information about RS232/RS485.

5. Pray to whatever Gods or Devils you believe in - hard. I've been dealing with this for 32 years, and "There ain't nuthin' standard about it".