I don't understand what you're trying yo say:
which part isn't clear ?
you mean that it could be possible that the intern architecture of the uC and CPLD to be different, even if they have the same part number ? Because if their internal architecture is identical, i don't see why the BK firmware won't work ...
And it's clear that a firmware update cand only modify the CPLD and/or microcontroller, because the rest are discrete components (like op-amps, CMOS 4000, 74HC series).
a CPLD is programmeble logic device, the actually used Altera MAX II EPM240xxx does have 192 logic macrocells.
So no just imagine you have 192 logic ICs, how many combination of function can you build with them ?
And now supprise, exact same problem for µC - it didn't matter what on the empty name is on the chip and
didn't matter how these two chips are interconnected, what's matter is the function inside.
There no indication that BK and Tonghui are using exact the same protocols, procedures or whatever
- the only common thing (if PCBs are really exact the same way routed) might be the measurments way.
I give you another (more visual) example, ATTEN and RIGOL DSOs - both looks from outside different, both have totally
different firmwares - but if you look inside they looks exact the same.
This means ATTEN might work properly if you burn RIGOL firmware (DSP and CPLD!!!) and vice versa
- and yes if you burn BK firmware into CPLD and µC the Tonghui device will work, and vice versa too.
But to be very honest, you can't actually do this.
Why ? Well, very simple, the firmware update on BK website doen NOT include CPLD code.
You maybe wondering now why, that's simple too - everybody who have CPLD and µC firmware
can easily produce own clones.
Even if Tonghui and BK would be (or are) designed by same developers team, it might happens that each of them
is using different checksum or protection in the bootloader (which is actually common practice for OEMs).
But hey, nothign simple like this, connect the Tonghui device to PC, connect via Terminal
and try to run the update - and you will see what happens.
Sur eit can be that both companies are lazy and bootloader will accept the code and CPLD will be programmed in exact
same way making the BK firmware working with no issues - but the chance is not that big.
If you brick the Tonghui, you will need at least to erase the µC before you send it back, lol