Temco Bootloader Dongle


As per Maurice, I am posting in hopes of getting a guide on using the bootloader dongle. Though it likely will be straightforward I want to be sure I am following best practices. I found on the board where I assume the bootloader plugs in, and again I am assuming I line up the white arrows (>) by J2 on dongle and between J3/R7 on Nano board (as shown in picture)?

For background, I have several T3-Nanos which were successfully updated over the network, however something happened during the process that seems to have jammed up the bootloader so I was sent this dongle to try to flash the original back onto it.

Thank you for the advice and being so helpful overall!

Crystal Patten

For the sake of forum searching and clarity of information, this was my original email with what I was seeing while troubleshooting. Love the searchable feature in the forum, it has solved many of my smaller issues!

"We have several T3-Nanos that I have been updating, programming, and installing, and unfortunately there seems to have been an issue during one of my firmware updates. The Nano in question stopped being reachable, and the BEAT LED does NOT turn on at all. No blinking or lights whatsoever on BEAT.

Power and Ether still light up, but 0 action on beat.

I connected to a working nano with the same setup just to be sure it was not a wiring issue. According to the post I found below, I believe this means it has been corrupted and will require outside help to fix"


With this info it was recommended that it is either a bootloader issue or a hardware issue, so we received the dongle to hopefully restore it vs. sending it back for replacement.

Great, our team will report back first thing in our morning.

  1. Connect the USB dongle to the T3-Nano as shown below, and then power the T3-Nano up.

  1. Open the mcuisp.exe file as shown below:

Select correct Serial Port, and the correct hex file for your MCU, files with the suffix ST are for ARM chips. Make sure the information in the bottom area is consistent with the picture
Click “Start ISP(P)” to start loading.

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I appreciate the guide! Can you direct me to the correct file to use for the T3-Nano bootloader repair? I connected to it and read the data for specifics, included in picture below:

I found a few options for files;

Thank you!

You only need to deal with the bootloader if the device is really messed up as in when you are doing development work for example. Possibly, the device is older there may be some new features such as doing updates over Bacnet. For the most part you never need to deal with updating of bootloaders. On later versions of our firmware the ISP update tool will detect the bootloader version and update it for you automatically, just update the firmware using T3000 → help → check for updates → update firmware and it’ll handle the details.

You can tell if the bootloader is corrupt by cycling power. The device should light up the heartbeat LED with two blips, repeating every second or so. The device may have an LCD in which case it’s the backlight which will be flickering. After about 15 seconds of this bootup ‘double blip’ phase the device will switch over to ‘normal’ mode with the heartbeat LED blinking with a single flash, repeating every second or so. If the device has an LCD it’ll bring up some text on the display. If you don’t see the device going to ‘normal’ mode then you can load firmware in the bootup phas using the ISPTool.

You rarely need to update the bootloader as I mentioned, its mainly for developers or very old devices.

If you do need to reload the bootloader, use the following file:

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Maurice, thank you for this further information and clarification, based on our previous conversation and the troubleshooting I have done I still believed it to be the bootloader so used the file that Lijun sent (thank you!), and my heartbeat LED is restored! This issue occurred during a firmware update that disconnected and failed, I tried running the regular Firmware file using the dongle but it didn’t correct the issue, however the ISP file did, and now I can reach and program my T3-Nano again. For my records, what would be the Bootloader file to use for the T3_XB_ESP? I received 2 of them and am going to begin testing them out very soon :slight_smile:

Thank you for all of the advice and the support given through this, much appreciated!


For T3_XB_ESP, the bootloader file is


This is the guidance document:
How to load the ISP for T3-Nano ESP32.pdf (237.3 KB)
Download tool here:

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