Over-the-Air (OTA) Firmware Update Guide (Draft)

The OTA Update feature of the VT132 enables you to update the firmware of your VT132 to the latest release without having to connect your VT132 to a PC via the FTDI connector or install any utilities on your PC to flash new firmware to the ESP32 module.

OTA updates are performed via the 'AT' (Hayes) Modem interface using a series of 'AT' command extensions.


From the modem prompt/command line you can type AT$ for help to be reminded of the OTA 'AT' commands.


You can connect to the modem from your RC2014 using a terminal program such as KERMIT or QTERM


You can enable the modem locally and connect directly from the VT100 to the modem in LOCAL mode. See the Quick Menu Guide for details.

The current firmware on GitHub is tagged as the latest release, so simply use the OTA update feature as follows:

From the modem prompt/command line:

  • AT+W+ or AT+W=ssid,pwd to join your Wi-Fi network
  • AT+U$ to see what firmware version you are currently running [optional]
  • AT+U? to query GitHub for the latest firmware image
  • should report V1.0.0 (or similar)
    • following the version number, a self explanatory indicator of [OLDER], [SAME] or [NEWER] will be shown
  • AT+U^ or AT+U! to upgrade or force the upgrade, depending on your current version
    • AT+U^ will only work if the queried firmware image is [NEWER]
    • during the upgrade process a series of full-stops ... will be output to indicate progress with the upgrade
    • when the upgrade completes downloading the new firmware image into flash memory the modem will respond with an OK
  • AT+U$ to see what firmware version you will boot next [optional]
  • H/W reset after success with the download & flash
    • the new firmware image will only be run following a H/W reset or reboot


Once you have entered the Query OTA Update command AT+U? the VT132 should not be expected to operate "normally" until you perform a H/W reset or reboot of the VT132.

This is because the Query OTA Update command opens and creates a number of files and large data structures in memory that may conflict with normal operation and these can only be closed and released by a H/W reset or reboot.


You can safely force upgrade AT+U! the firmware to the same version you are currently running if you simply want to "practice" the upgrade process.

Example output from the Show OTA Partition Status AT+U$ and Query OTA Update AT+U? commands is show here:

OTA AT Commands

A full description of the OTA Update commands and their output will be added here later: TBA.

Update to a version from a local web server


For the security conscious

For the security conscious

OTA Updates from GitHub are performed using the https protocol.

Security certificates (Root CA) for GitHub and Amazon S3 (where GitHub stores release binary files) are embedded in the firmware.

https requests to servers that use any other Root CA certificate will fail to authenticate.

Also, the VT132 makes this request as an https client and does not implement an http or https server.

Note also:

  • A Wi-Fi connection to an Access Point is never established by default, but must be explicitly (re)connected using the AT+W= or AT+W+ commands
  • The only time the VT132 makes outgoing IP socket requests is when:
    • you dial a host with the ATD dial command
    • you initiate an OTA update transaction with the AT+U? Query OTA Update command and the subsequent AT+U^ or AT+U! upgrade or force upgrade commands
  • The only time the VT132 accepts incoming IP socket requests is when the modem is enabled for "Answer" mode with AT&A (not be default).
Last Updated: 7/26/2020, 1:52:54 PM