Help reverse engineer Polar Instruments T4128 Serial Port DSUB9 connector.

[aqibi2000]

Hi all,

I’ve recently acquired a Polar T4128, there is zero information online with regards to the operation, use or service.

It uses a very particular pin out for the Serial Comms to the computer. Does anyone own any Polar equipment which uses the DSUB9 maybe it uses the same pinout as my unit?

I have opened it and done continuity tests from the 2 separate HIN232CP (similar to Max233) ICs used. (It’s not just 1 tx, rx and Gnd).

In need help reverse engineering this to work, have USB Serial comms equipment I can connect on the logic side the the transceivers as well as an Oscilloscope

A very crude pinout if the DSUB9 is attached which I made.


 
Thank you

[pbarton]

Probably like this....
http://www.usconverters.com/index.php?main_page=page&id=61

[aqibi2000]

I have gone through pin by and thus created the below pinout of the DSUB9–>Logic Converter RS232 —> UART

I have not completed the reverse engineering of the optocoupler circuit however which involves some Schmitt triggers etc.

The issue I can foresee is many of the UART pins are active low so I will need to build some form on logic inverter to use with a regular off the shelf interface. Any thoughts on this? Discovered a RT232BM and RT232R

Table below shows a comparison to the regular RS232 interface pins to what I have been tracing around the dual layer board

Could I face some issues with using the supplied software with regrads to the VID/PID from the FTDI and what can I do about this?

[pbarton]

I looked at the original listing of https://www.ebay.co.uk/itm/293421075479
And I had a much better understanding of….
1. Your belief that the 9 pin cable is special.
2. the supplied software

I think that your expectation that the cable needs to be reverse engineered is overkill.
It’s a regular 9 pin RS232 null-modem cable (where Tx->Rx and Rx->Tx), rather than a ‘straight’ cable.
That’s probably the only thing that is special about it.

The application probably requires the signals…..
Data Terminal Ready and the response Data Set Ready also
Request To Send and the response Clear To Send, to be conveyed.
Your Polar Instruments T4128 should not care if Carrier Detect and Ring Indicator are in the cable or not (they are tied up locally).
These signals are obsolete (and unnecessary if you are not using modems to dial across the PSTN).
I don’t envisage a problem with your USB to RS232 converter/dongle.
The application software will probably require you to set a particular port number and baud rate.
Good luck with the kitchen extension.

[aqibi2000]

It became clear after following the pins to the UART from the DSUB that only the following were relevant:
     •Data Terminal Ready and the response Data Set Ready, Request To Send and the response Clear To Send.


Agreed, the following are not used for anything :  CD is held at 5V and RI is held at 0V permanently.


By reverse engineering I literally just meant find the pinout, as you can see I found the allocation was only standard for Gnd tx and rx.
Thank you for your support, much appreciated