Serial Decoding Help - Page 1
Forum section: electronics / projects

author: VintageTech
author_rank: Contributor
timestamp: March 14, 2015, 08:06:44 pm
content: Today I was trying to decode a serial two wire serial steam when I came across something odd. The waveform that I was getting looked nothing like UART or I2C (no clock). I tried to hook it up to a UART source (Arduino) and send bytes through the serial terminal The only thing that happened was a continuous stream of zeros appeared on the screen (I tried adjusting baud rate). So, I continued to debug and looked up timing diagrams to try to find something that matched. No luck. With out anything to go off of, I figured that it would be a good idea to post on the forums, as the people here have much more knowledge than I do.Thanks,VintageTech

author: Howardlong
author_rank: Super Contributor
timestamp: March 14, 2015, 08:23:06 pm
content: Quote from: VintageTech on March 14, 2015, 08:06:44 pmIt looks like it may be an I2C clock to me.Edit: hmm, not certain. Do you have more details including your source code?

author: tautech
author_rank: Super Contributor
timestamp: March 14, 2015, 08:33:08 pm
content: I'm no expert in this regard, the only stuff I've done was experimenting with decoding with my SDS2304.What I learnt was to identify the chips for a greater understanding of what to expect.Some customers routinely check their serial streams just as you have done but with an intimate knowledge of their design and programming to refer to.You have an "idle high" stream, but in datasheets sometimes it is refered to as "active low".Examine the circuitry for settings of clock speed and that will help for identification of streams.

author: mikerj
author_rank: Super Contributor
timestamp: March 14, 2015, 08:42:51 pm
content: Quote from: VintageTech on March 14, 2015, 08:06:44 pmYou said it was a two wire serial stream, but that there was no clock. What is on the other wire?

author: miguelvp
author_rank: Super Contributor
timestamp: March 14, 2015, 09:22:17 pm
content: Looks like the SDA signal from I2C, there must be a SCL somewhere around.Hard to tell but it seems to be two bytes (16 bits) worth of data in there.Edit: not the best capture of an I2C

author: Howardlong
author_rank: Super Contributor
timestamp: March 14, 2015, 09:50:17 pm
content: I was thinking it was the clock from a software I2C, it was the right number of edges for one byte.

author: hamdi.tn
author_rank: Frequent Contributor
timestamp: March 14, 2015, 09:52:02 pm
content: look like 2 bytes uart to me , no need for clock with uart !

author: VintageTech
author_rank: Contributor
timestamp: March 14, 2015, 10:23:27 pm
content: Quote from: mikerj on March 14, 2015, 08:42:51 pmI think i have my terminology wrong. My apologies. There are two separate wires with the initial waveform on one and nothing on the other. This leads me to believe this is some sort of UART or I2C line. But there is no clock and it doesn't look like the UART I'm used to on the scope (baud rate?) and it connects to a GPIO pin on the micro, ATMEGA32L, which has I2C but isn't connected to anything that I'm aware of.

author: VintageTech
author_rank: Contributor
timestamp: March 14, 2015, 10:38:28 pm
content: I probably should add some detail about what I am trying to do. I am attempting to figure out a way to send data to a driver board that was pulled out of an induction cooktop. (Motor Driver maybe?) The board has Four large IGBT's that drive induction coils. The power delivery section of the control board catastrophically failed with a loud pop while boiling water one evening. I was hoping to utilize the drivers (Which still work). In order to do that I need to reverse engineer the protocol, which may mean simply finding a way to reprogram them.

author: hamdi.tn
author_rank: Frequent Contributor
timestamp: March 14, 2015, 10:57:08 pm
content: if it's uart i will say 4800 baud and 4 bytes

author: Howardlong
author_rank: Super Contributor
timestamp: March 14, 2015, 11:00:49 pm
content: I agree, it looks about 4800 baud, but where is the stop bit on the first byte?Edit: the second line, is it high or low?

author: VintageTech
author_rank: Contributor
timestamp: March 15, 2015, 12:02:47 am
content: Quote from: Howardlong on March 14, 2015, 11:00:49 pmThe second line is always low. I will try again to capture serial data at 4800 baud when I get the chance. I am very new at serial decoding and my oscilloscope doesn't have it built in. I guess I'll have to figure it out by hand

author: zapta
author_rank: Super Contributor
timestamp: March 15, 2015, 03:50:50 am
content: Quote from: VintageTech on March 14, 2015, 08:06:44 pmThis picture reminds me linbus, a long break follows by a 0x55 clock synchronization byte. It's not automative though and not 12V.