Capturing data from TTL-232R-3V3

asked 2022-09-14 15:25:58 +0000

I'm trying to capture RS-232 data from a TTL-232R-3V3 USB to serial converter. I'm using Windows 10, and it shows up as COM5.

My USBPcap interface options (for USBPcap1) are as follows:

Snapshot length: 65535
Capture buffer length: 1048576
Capture from all devices connected is checked
Capture from newly connected devices is checked
Inject already connected devices descriptors into capture is checked

There are multiple devices showing in "Attached USB Devices" but I only have [5] USB Serial Convert / USB Serial Port (COM5) checked.

Most of these settings were the default - I will try again with some of these options unchecked, though I would think since I only selected the one device from the list they shouldn't matter. I'm posting the question now as I won't have an opportunity to test again until tomorrow.

I found an example PCAP from the old bugzilla site (filename: TTL-232R-3V3-USBPcap-control.pcapng) that someone else used the same adapter to capture, and when I open that PCAP file it at least identifies the protocol as FTDI FT.

However, the captures I have don't seem to even identify that. In fact, the captures I have don't even advance the time. They all have 0.000000. I would upload my file, but I just created a new account (my old account doesn't work anymore) and it says I need 60 points to upload.

I tried setting "Decode As..." to USB device, FTDI FT but that didn't change anything in the display of my capture files.

I've used Wireshark for ethernet captures in the past and know how to do that very well, but I've never used it on serial comms before. I can't seem to get ANY program to work for that right now. Other programs I've tried are not able to connect (I believe due to Windows 10 compatibility issues - I've tried compatibility mode but that didn't work either.)

Wireshark is at least showing SOME data, but I'm not sure if the data I have is any good - it's certainly not the data I'm expecting. I don't know what the TTL-232R-3V3 is wrapping the RS-232 data in.

The RS-232 device it's connected to has the following settings:

Bits Per Second: 9600
Data Bits: 8
Parity: None
Start Bits: 1
Stop Bits: 1
Bit Sequence: StartBit LSB ---- MSB StopBit

It sends 28 bytes per package, a package is sent every 100 ms

How do I set up USBpcap to properly decode this data?

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Update: Dug further into my PCAP file. What it consists of is the device identifications and configurations of the devices on the USB Bus. Definitely need to uncheck "Capture from all devices connected" and probably want to uncheck the other two options as well to filter out unwanted "noise". That being said, one of the device identifications showed idVendor = 0x0403 which is "Future Technology Devices International, Ltd." so this definitely is an FTDI device. That being said, there is no sign of the actual RS-232 data in the captures.

Trashman gravatar imageTrashman ( 2022-09-14 19:08:00 +0000 )edit