Need help using RS232 logger software with serial devices

Serial Communication
1

I’m trying to capture and analyze serial data from a few RS232 devices using RS232 logger software, but I’m not getting the output I expect. Some data seems to be missing or garbled, and I’m not sure if my settings (baud rate, parity, stop bits, etc.) are correct or if I’m using the wrong type of logger. Can someone explain how to properly set up and use RS232 logger software for reliable data logging, and what key settings or common pitfalls I should check first?

2

First thing to check is the basics. Wrong line settings will give you missing or garbled data every time.

Go through this list step by step:

  1. Match serial settings on both ends
    Baud rate
    Data bits (often 8)
    Parity (None, Even, Odd)
    Stop bits (1 or 2)
    Flow control (None, RTS/CTS, XON/XOFF)

If any of those differ, you get junk or partial data. Do not trust labels, read device manuals.

  1. Check your wiring
    Are you using a straight cable vs null modem where needed
    RS232 levels, not TTL or RS485
    Common pins: 2, 3, 5 on DB9, check if device is DCE or DTE
    Try a different USB to RS232 adapter if you use one. Some cheap ones drop bytes under load.

  2. Test with a known simple setup
    Set up a loopback on your COM port. Short TX and RX, then type in your terminal.
    If your logger shows exactly what you type, the PC side looks fine.
    If not, try different baud and flow settings until it stabilizes.

  3. Check logger options
    Some RS232 logger tools buffer or apply filters.
    Turn off line translation, timestamp insertion, or protocol decoding at first.
    Log raw hex data and compare with ASCII output. If hex looks complete but text looks broken, it is decoding, not the line.

  4. Stop using multiple apps on the same COM port
    Only one program should own the serial port at once.
    Close all other terminal or logger tools before you start.

  5. Try a different monitoring tool
    A dedicated serial sniffer helps a lot.
    Serial Port Monitor is useful if you want to see multiple sessions, monitor read/write events, and decode protocols while your main app runs.

If you want to focus on logging and decoding, something like an advanced RS232 logging solution helps keep long term logs, split sessions, and export to CSV for analysis. This type of software is described well here:
advanced RS232 serial data logging tool

Set your baud low at first, for example 9600, no parity, 8 data bits, 1 stop bit, no flow control. Confirm clean output there, then match whatever the device manual states. If data still looks bad, post your exact settings and cable type.

Need help using RS232 logger software with serial devices
Need help using RS232 logger software with serial devices1536×625 116 KB

3

Baud/parity/etc. are the obvious suspects and @viajantedoceu already nailed most of that, so I’ll skip repeating the same checklist and poke at the less obvious stuff that often causes “missing” or garbled serial data.

  1. Check for partial frames & timing gaps
    A lot of RS232 devices don’t stream bytes continuously. They send short frames with gaps in between. Some loggers have:

    • “Packetization timeout” or “Inter‑byte timeout”
    • “New line on gap > X ms”
      If that’s set too low, the logger will split one logical frame into several lines, which looks like junk or missing data.
      Try: disable “smart packetization” or similar features and just record a raw continuous stream first.

  2. Turn off auto‑baud / auto‑detect features
    Some tools try to guess baud rate or framing from the input. That can work on clean lab setups and fail miserably with noisy or bursty devices.
    Set the serial params manually and turn off anything labeled “auto detect,” “auto config,” or “synchronize with device.”

  3. Check character encoding & end of line handling

    • Device might be sending plain binary or some proprietary protocol, not ASCII. Your logger may be trying to show it as text, making it look like garbage.
    • Switch the view to “HEX + ASCII” and compare. If HEX looks consistent, the line settings are fine and what you’re seeing is just non‑printable data.
    • Also check CR/LF options. Some tools replace CR or LF with spaces or ignore them, which can make messages run together.

  4. Buffer overruns & logger performance
    This is where I slightly disagree with the “just lower the baud rate” approach. If your real device uses 115200 or faster, it’s better to test at the actual speed and verify that both your USB‑RS232 dongle and logging software can keep up.
    Signs of overrun:

    • Random missing bytes in the middle of otherwise valid frames
    • Logger UI freezing or lagging when data bursts happen
      Solutions:
    • Use a better USB‑RS232 adapter (FTDI or similar usually behaves better).
    • In your logger, reduce “UI refresh rate” or turn off fancy live decoding and just dump to file.
    • If possible, run the test on a machine that is not already CPU‑starved.

  5. Hardware handshaking vs. actual wiring
    Even if you set “No flow control” in software, some devices still expect RTS/CTS or at least DTR/DSR in a certain state or they throttle / drop data.

    • Check if your cable really carries RTS/CTS lines. A lot of cheap “RS232” cables only wire TX/RX/GND.
    • Some hardware will silently stop talking if CTS is not asserted.
      Try explicitly enabling RTS/CTS in both the device and the logger if your cable supports it, or force the modem control lines high with a jumper adapter if needed.

  6. DTE vs DCE confusion at the signal level
    It’s not just pin 2 vs pin 3. Some devices marketed as “RS232” are actually TTL‑level behind a weird adapter. If you went PC USB‑RS232 → some RS232–TTL cable → device, signal levels might not match and can cause borderline, timing‑sensitive corruption.
    If this is a dev board or embedded thing:

    • Confirm whether it needs real ±12 V RS232 or TTL (3.3 V / 5 V).
    • If it’s TTL, use a USB‑TTL adapter instead of an RS232 one.

  7. Verification with a second tool in “sniffer” mode
    Not talking about using multiple apps on the same COM simultaneously as a client, that’s bad. But if you want to confirm that your logger is not the one messing up:

    • Use a sniffer like Serial Port Monitor that can sit between your app and the port (or use its “monitor” mode).
    • Check the “captured” data vs what your main logger shows. If Serial Port Monitor shows clean frames but your logger log looks broken, you’ve found the culprit.
      Serial Port Monitor is also nice if you want to see each Read/Write with timestamps and exact bytes, which helps a lot when diagnosing “missing” chunks.

  8. Time‑stamping resolution & ordering
    Some loggers have low‑resolution timestamps and then sort lines by that coarse timestamp. With quick bursts from several devices or from bidirectional traffic, lines might appear out of order, which feels like data is corrupted.
    Look for options like “high‑resolution timestamp” or “log events in arrival order” rather than by second‑level timestamps.

  9. Try a direct PC‑to‑PC test to isolate device vs logger
    If you have another PC or laptop with a serial port (or another USB‑RS232 adapter):

    • Connect them with the correct null‑modem wiring.
    • Use a basic terminal on one side sending known text patterns (e.g. ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789 in a loop).
    • Log that with your RS232 logger on the other side.
      If the pattern is perfect, your PC/logger combo is fine and the device or cabling to the device is guilty. If bytes go missing even in that simple loop, focus on your adapter/driver/logger stack.

  10. About the “logger app download” bit
    Since you’re clearly experimenting with tools, check out something like:
    Get advanced serial logging utilities here
    That kind of package plus Serial Port Monitor gives you a more robust environment for long‑term captures, protocol decoding, and side‑by‑side HEX/ASCII comparison than many basic freebie loggers.

If you can, post:

  • Exact serial params from the device manual
  • Which USB‑RS232 adapter chipset you’re using
  • A short HEX dump from your capture (like 50–100 bytes)

With that, it’s usually possible to tell if you’re looking at pure framing issues, buffer drops, or simply binary data that your logger is trying to interpret as text.

2 Likes
4

Skip the basics already covered by @espritlibre and @viajantedoceu for a second and think about what you’re actually trying to see.

A lot of RS232 “garbage” logs are not line‑setting issues but mismatched expectations between:

  • What the device sends (binary protocol vs human‑readable text)
  • What the logger tries to present (ASCII, line‑based, packetized view)

Try this angle:

  1. Decide: are you sniffing a protocol, or debugging bytes?
    If you just need every single byte to be correct, ignore higher‑level structure. Configure your tool to record raw stream to file, no packetization, no CR/LF translation, and view in hex. Only after you confirm byte‑perfect capture should you worry about pretty text.

  2. Use two tools with different philosophies
    One mistake is using only a “terminal style” logger. Grab something like Serial Port Monitor and compare. It is good at:

    • Showing each read/write with timestamps
    • Splitting traffic by direction
    • Saving hex logs for later parsing
      Pros of Serial Port Monitor:
    • Clear separation of app→device and device→app
    • Solid for long sessions and protocol analysis
    • Nice if you want to reverse engineer framing
      Cons:
    • Windows only
    • Can feel heavy if all you want is a quick “does it talk?” test
    • Learning curve if you only need simple logging

    Use your RS232 logger for “human view,” and Serial Port Monitor for “forensic view.” If bytes are missing in both, suspect wiring or handshaking. If one is clean and the other not, you have a software interpretation problem.

  3. Don’t blindly trust “device manual” examples
    Small disagreement with the “just match the manual” advice: some manuals are wrong or out of date. If you suspect that, systematically scan baud/parity combos while logging hex and watching for a stable, repeating pattern. When you hit the right settings, patterns lock in and the data becomes consistent.

  4. Check directionality & who owns the conversation
    If the device mostly responds rather than streams, and there is no proper host app talking to it, you might only see sporadic bytes (like status beacons) and think data is missing. In that case:

    • Run the vendor’s configuration utility or host software and let that drive the device.
    • Attach Serial Port Monitor to the same port to see the full command/response protocol in the background.

  5. Think about long captures & edge cases
    If you are logging for hours, test wrap‑around and file size limits. Some lightweight loggers quietly rotate or truncate logs, which looks like “missing data” over long periods. Serial Port Monitor and similar tools usually handle large logs better, but still verify:

    • Max file size options
    • Whether they drop data if the disk is slow or full

  6. Interpret the “garbled” part carefully
    If the hex stream is consistent but the ASCII column looks like random symbols, that often means the device is binary: CRC bytes, length fields, etc. In that case, your next step is protocol decoding, not more fiddling with baud. Compare multiple frames, line them up by an obvious sync byte or header, and you can often reverse engineer structure.

If you can share a short hex snippet plus device model and current log setup, people can usually tell in a few lines whether you are looking at framing errors or just misinterpreted binary.