Author Topic: Identifying the MCU from RT85 handheld Radio  (Read 231 times)

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Offline Cassus

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Identifying the MCU from RT85 handheld Radio
« on: June 11, 2021, 03:36:29 pm »
Hello,

I am trying to reverse engineer a RT85 Retevis handheld radio in order to produce a custom firmware. The main problem I have is to figure out the microcontroller they are using. They went through the effort of grinding the top of the chip to make it harder for people to guess what it is.
The remains of a logo is still distinguishable on the bottom of the chip. Does anyone recognize a brand logo? I doubt it is an obscure Chinese manufacturer otherwise they would have tried to mask it.

Also, the programming port has only 4 pins so I guess VDD, VSS, Data and Reset. That already excludes some brands like Microchip which uses at least 5 pins.

I have access to a J-Link, ST-Link, ICD3, Oscilloscope and Logic Analyzer if that can help.


here are the pictures:









BTW, The TH-UV88 handheld radio from TYT uses the same PCB and doesn't erase the markings so if anyone has one lying around...
 

Offline geggi1

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Re: Identifying the MCU from RT85 handheld Radio
« Reply #1 on: June 11, 2021, 08:08:18 pm »
I guess this is a game of elimination.
Start finding possible candidates for MCU same packages is a good start.
Reverse engineer the circuit around the MCU to find pins that are detectable like power, gnd, databusses for cummunication to other devices and programming of the radio.
Do the elimination by checking datasheets for the possible candidates.
 

Offline Cassus

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Re: Identifying the MCU from RT85 handheld Radio
« Reply #2 on: June 12, 2021, 08:08:59 am »
the problem with the package is that there is an insane number of different MCU when you dig a little. There are the common brands like Microchip, Atmel and STM but tons of small ones too. that's like finding a needle in a hailstack.

+ the remains of the logo kinda looks familiar so that's even more frustrating
 

Offline Cassus

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Re: Identifying the MCU from RT85 handheld Radio
« Reply #3 on: June 12, 2021, 09:25:58 am »
I think I found the logo. it is similar to the one from another chip on the PCB. that make sense that they would use chips from the same manufacturer.
can't find any infos on any QFP 48 chip on Beken's website though

« Last Edit: June 12, 2021, 09:33:12 am by Cassus »
 

Offline amyk

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Re: Identifying the MCU from RT85 handheld Radio
« Reply #4 on: June 14, 2021, 01:25:30 pm »
That's because it's a QFN32...

http://antena.fe.uni-lj.si/literatura/Razno/BK4815/BK4815N_Datasheet_v1.0.1.pdf

But Beken don't make MCUs. I'd say the erased logo looks more like Silabs or Cypress.
 


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