I'm working with a Digi Connect ME serial to Ethernet bridge, which runs a "Plug and Play" firmware by default.
The specific product page is here. The part number is DC-ME-01T-S. It appears to be an ARM based board - a NS7520 specifically. This is not the product with NET+OS or a JTAG port.
The support page is here - contains firmware, documentation, drivers.
Digi provide .bin files, but no source code.
I am trying to unpack the .bin files but I am not having much luck. binwalk doesn't pick up anything, mkimage from u-boot doesn't find the magic number (some other Digi products use U-boot), file just indicates it is data.
There seem to be two firmwares - the large EOS file and a smaller POST file. I suspect the POST one might be a bootloader - it doesn't look compressed.
Here is a link to the most recent EOS firmware: http://ftp1.digi.com/support/firmware/82001120_M.bin
And the post firmware: http://ftp1.digi.com/support/firmware/82000867_H.bin
Entropy analysis of the EOS firmware shows high entropy throughout the file.
The NET+OS version of the Digi Connect ME runs Digi's NET+OS network operating system which is based on ThreadX's RTOS. I am not sure if the Plug and Play firmware is just a specific variant of this.
The Digi Connect Me is used in a lot of embedded devices to provide network connectivity and a lot of them are open to the Internet, hence the interest.
It's not like anything I have seen before.
My first goal is to run strings against the firmware as I suspect it has undocumented functionality when running in modem emulation mode.