Help with Analyzing RS232 Voltage Data Recorded in a CSV File

I recently performed an RS232 communication test and recorded some voltage data. The interface was RS232, and I transmitted the character "H". The transmission settings were 1 start bit, 1 stop bit, no parity, and 8 data bits. The baud rate was set to 9600, and the sample frequency was 200ksps. The voltage data was saved as a comma-separated values (CSV) file. I'm trying to analyze this data and would appreciate help in interpreting the recorded voltage levels, given the sample rate and transmission settings. Specifically, I want to know how to extract the bit information from the voltage data for the transmitted character "H". Can anyone provide insight into how to work with this data and reconstruct the transmitted bits?

Thank you!

[dpb]

"... help in interpreting the recorded voltage levels, given the sample rate and transmission settings. Specifically, I want to know how to extract the bit information from the voltage data..."

That's going to be totally dependent upon what the device transmits. That will be documented by the vendor of the instrument.

[Michael Liedlgruber]

Sounds to me like you are trying to solve some homework assignment so I may be to late with my advice anyways. But gather some knowledge on the RS232 protocol and the meaning of the different transmission settings. Then it's fairly easy to reconstruct your character from the recorded voltage levels.

@dpb: if we are talking about recorded voltage levels from a RS232 communication, vendor information is not needed in my opinion. Everything needed is defined in the RS232 standard.

[dpb]

@Michael Liedlgruber the transmission protocol may be defined, but what the instrument actually sends and how it encodes the voltage values is entirely up to the vendor...it's possible the voltages are sent as a decimal string of digits, yes, but often what one gets are counts or just bytes of some fixed-pt floating system instead.

[Michael Liedlgruber]

@dpb Oh yes, that‘s of course true. I assumed that the OP was able to read the voltage levels properly but that he was not able to decode the signal due to lack of knowledge of the RS232 protocol.

[dpb]

I fail to understand how "OP was able to read the voltage levels properly but that he was not able to decode the signal " if didn't understand the protocol; seems as though that would stop him/her at the very beginning in being able to return anything?

My presumption is he had the returned data but didn't know how to convert those to the actual voltages.

[Walter Roberson]

it's possible the voltages are sent as a decimal string of digits,

No, the user explicitly said that the character 'H' was being transmitted over RS232. RS232 defines the protocol -- start bit, data, stop bit. Wikipedia says

Valid signals are either in the range of +3 to +15 volts or the range −3 to −15 volts

with respect to the "Common Ground" (GND) pin; consequently, the range between −3

and +3 volts is not a valid RS-232 level. For data transmission lines (TxD, RxD, and

their secondary channel equivalents), logic one is represented as a negative voltage

and the signal condition is called "mark". Logic zero is signaled with a positive

voltage and the signal condition is termed "space".

Start bits are logic 0 (so, positive voltage) and stop bits are logic 1 (so, negative voltage.)

Bits are sent least significant first (so reverse of the typical order of writing.)

Presuming ASCII, that would make the bit order

['0', fliplr(dec2bin('H')), '1']

ans = '000010011'

and the voltage levels

regexprep(ans, {'0', '1'}, {'H', 'L'})

ans = 'HHHHLHHLL'

Nothing all that complicated about it.

[dpb]

I guess I whiffed on the missive, Walter...I thought the OP had a CSV file of data from an instrument and didn't understand how to interpret that...should have read more than the title more thoroughly...