Hey
I have a wireless ISS that I want to run a cabled and read the data from an Arduino. However, I am having issues getting any "data".
Since it's a wireless ISS, it doesn't have the ADM348 RS-422/RS-485 chip U91. I soldered one in, hoping that was all what was needed to get the data out of the RJ11 jack. Strangely enough, that was not the case.
What comes out of the two central lines of the RJ11 jack does not seem to be an RS-422 protocol. First I have tried a RS-422/USB converter set to 4,800 baud 8N1, but got only <BREAK> signals all over. They are repeating every 2.5 seconds or so. After looking at the stream with an oscilloscope, the signal is quite strange.
The signal seems to start with something like a large start bit, then followed by alternating highs and lows (or 1 and 0 bits, much like the byte 0x55). The strange thing is that the "bits" are 26us long, which relates exactly to 38,400 baud rate. And indeed, if I connect with a terminal set to 38,400 8N1, then I see a good RS-422 protocol, no breaks and frame errors, but the incoming data is 0x55, 0x55, etc. Which is not the data I was expecting.
Now I thought let's see what's coming out of the MCU into the DI pin (pin #4) of ADM348, or in other words what exactly is the MCU sending out as data. And guess what, the MCU is sending exactly this data. So the ADM348 chip I soldered is not damaged, it's working as expected. I have observed the orientation, pins and everything. Verified that VCC (pin #8) is indeed tied to VCC, ground is good, even DE (pin #3) is set to high to enable output. Everything looks fine, except the data itself.
Perhaps the firmware is quite different for cabled and wireless ISS. Does anyone have any experience converting a wireless ISS to cabled?
I'm attaching some screenshots to illustrate my findings.
D0 is on the DI pin of ADM348
D1 is on the A line of the RJ11 jack.
Cheers
Mladen