Viewing RS-232 Commands/Strings

jabramson

What's the best way to capture a rs-232 string from a device? (The Serial commands are unknown, so I'm trying to "capture" them.) Tried hooking it into the terminal port on my computer and viewed in Netlinx studio. I could see the commands, but they are all gibberish, nothing remotely related to hex or ascii. Also tried Hex Com Tool with the same results.

Here are a couple of the strings if you want to take a crack (captured with Hex Com Tool, switched between ASCII and HEX)

188066666698189800E680
1E98608698E680
18806666669898E09800E680
1E98608698E680

or 

(18)(80)fff(98)(18)(98)(00)æ(80)
(1E)(98)(60)(86)(98)æ(80)
(18)(80)fff(98)(98)à(98)(00)æ(80)
(1E)(98)(60)(86)(98)æ(80)

I also tried capturing from a known device (Extron Router which uses ascii strings) and it gave me the same gibberish

John Nagy

Could your baud, bits, or parity be wrong? Those are excellent ways to make gibberish out of good data.

PhreaK

What you're seeing there isn't gibberish at all. In the first example you posted it has each byte represented in hex (1 byte == 2 hex chars). The second example is the exact same data, however bytes that have a printable character equivalent in the UTF-8 character set have been shown as that character and non printable characters shown as there hex value within brackets.

If you were not seeing the data you were expecting from your known device (Extron switcher) you may have set an incorrect baud rate. In serial communication data is sent as a time-series of bits. That is, there is a voltage that alternates between two states which relate to either a high or low bit. The buad rate defines the number of times per second that this state is observed. If both devices involved in the communication are not speaking at the same baud rate then its a bit like watching a pendulum lit only by a slow strobe light. You'll see the pendulum move, but the motion you see may be wildly different to what is actually happening. The equivalent in computer terms results in data corruption.