Need help understanding TTL and Arduino

Hello Group,

I am working on a project that involves reading a data stream, converting the data to a different format then outputting it to a serial port to connect to a PC for further processing. The transmitting device sends a constant stream of data and the receivers normally process the data. This is used to light a matrix of lights on a sign all controlled by the transmitting device. These lights are to signal when a process has been completed.

The cable that runs to the devices are a two pin cable, like phone cable. Some say it is running RS-485. After looking at the circuit board, I see that the data is basically a TTL configuration. I did measure with a scope and get 5V. I purchased a TTL-Serial/USB converter but can not seem to find the right data. This system is a very old technology and has been around for over 20 years so documentation is not an option. The company who made it is no longer in business. I am trying to modernize it by interfacing with it to output to a tv screen. Eventually, we will completely change the system with something but until then, I need this quick fix. So, this brings up some questions.

  1. How do I determine the speed of the TTL data?
  2. How do I determine the speed of the serial port?
  3. Do the TTL speed and RS-232 speed need to match? Buffering?
  4. Is it possible to have the arduino read the TTL data stream and display via console?
  5. Can the arduino be setup to be a capture device? protocol analyzer?

Thanks boB

If you have access to a logic analyzer set the it to decode async data, auto baud to see what you can conclude.

Can you see what chips it's using. Their part numbers could be a bit of a giveaway.

Thanks for the reply guys. I was able to get access to the main board after work hours and found out some more information. I followed the traces on the board to a micro controller. I looked up the data sheet and it shows those pins as "GPIO USART1/SPI mode".

I don't have a logic analyzer. :(


It's probably worth a shot just wiring it up to the SPI bus of the arduino and throwing some numbers at it. By trial and error you'll likely be able to get the values for CPOL and CPHA. (there's only 4 possible combinations). It may be as simple as just sending telex style output to it. In fact I'd put money on it.

You can try reading the data with the Arduino Rx serial port at different speeds and send it to the PC via the Tx port, see if any of the data makes sense. Trouble is, the serial port Will read the data and it Will output something - how you decide whether it makes sense or not is up to you.