I need to change the firmware of a Xbee3 to support 802.15.4. I have both:
https://www.sparkfun.com/products/13225
https://www.sparkfun.com/products/11812
But It seems that the usb board doesnt support changing firmware (since it doesn’t have a DTR signal), and I can’t find a computer with a RS232 D9 port (it seems they dont make them anymore). Is there any solution to changing the firmware of Xbee modules?
The two boards you have are what are called Breakout boards and not a development board. The fastest solution is to obtain an XBIB-U-Dev development board. This would allow you to do it.
You could also obtain a USB to RS232 adapter board but without the DTR line, that could be an issue.
Another option is to follow the steps outlined at https://www.digi.com/resources/documentation/digidocs/90001539/#concepts/c_xbee_bootloader.htm%3FTocPath%3DConfigure%2520the%2520XBee%25203%2520Zigbee%2520RF%2520Module|_____5 to manually enter the bootloader and upload the needed firmware file via XModem.