Reusing / repurposing MCU's on PCB's ?

[MathWizard]

For example, I have a nice 16-bit MCU, that uses C-languange, it's on a TV PCB, with RAM/ROM chips, and lot's of easy places to connect to the MCU traces, once the other chips and passive's are removed.

For a typical commercial product MCU, is it hard to erase the internal ROM/RAM on MCU's ? Are they sometimes fused off so you can't erase/reprogram them ? Or maybe you need a special machine just for a certain chip ? Or maybe only top level hackers and programmers can do this, and no one else bothers ??

I'm just wondering for down the road when I get way more into MCU's. Since it's already on a PCB, with lot's of traces and RAM. If the MCU can't be reprogrammed, I think I could get a new, blank one, and at least reuse the PCB.

[Fire Doger]

is it hard to erase the internal ROM/RAM on MCU's ?
Depends on the MCU.

Are they sometimes fused off so you can't erase/reprogram them ?
Yes

Or maybe you need a special machine just for a certain chip ?
Each mcu family has their own programming tools.

Or maybe only top level hackers and programmers can do this, and no one else bothers ??
You are not hacking anything, you are recycling the chip.
There is a huge market in china with reused parts.

You can just buy a development board to learn, no-one uses products as dev boards, the amount of time to reverse engineer it doesn't worth it.

[DavidAlfa]

Does it make any sense when you can get a small mcu board with a well known architecture for $4 at aliexpress?

[Andy Chee]

I once repurposed a salvaged 68HC711E9 OTPROM, by running it in expanded multiplexed mode, essentially becoming an HC11E0 (which uses external ROM).  I've also salvaged the odd PIC18F and Atmels/Attiny.  These can be erased even with the security bit set (which only prevents dumping the code, not chip erasure).

So yes it's possible to repurpose MCUs for experimenting with.  Is it worth it?  There's zero monetary value in doing so (unless you're a massive Chinese e-waste recycler), so the only value is personal knowledge and skills gained.

[Doctorandus_P]

It is not very common for microcontrollers to be completely locked. Most have some safety features that prevents the code in them from being read out, but almost always you can do a full erase that both erases the code and resets those features.

There is a lot of very cheap equipment from Ebay / Ali / China that uses STM32 (or clones). For example the Gophert power supplies, ESC speed controllers, FX2N PLC boards, Electronic loads, power supply modules, solder iron controllers and many more, and the microcontrollers on these boards usually just need two wires (+ GND) to erase them and reprogram them.

But when it comes to some random 16-bit microcontroller on some random consumer electronics board, then it's just not worth the effort. Setting up a toolchain, sourcing a programmer, learning how the peripherals of a uC family work all take a lot of time. It may even be very difficult to get datasheets for microcontrollers used in high volume consumer electronics. And when you can get it to work... What if you have spend 200 hours getting it to work and writing a program for the thing, and then you want to get another and you can't buy the part? There are literally thousands of microcontrollers you can buy for less than EUR2. The smaller ones start somewhere between 30ct and 50ct, and you can also buy lot's of them on breadboard friendly breakout boards.

[hans]

I'm a bit confused. Does this chip have internal or external ROM? If external, there is nothing stopping you from placing another ROM chip in there.
The question is whether you can find the tools to program those chips, and have a compiler for it.

MCUs with internal ROM can often still be reflashed if only read protection is turned on. However, some MCUs completely disable the debug port as an added layer of security, and in that case the chip is useless.

But to be honest, its probably not worth the time. The transferable skills is limited from an undocumented board with perhaps an ancient architecture. You can get Arduino/ESP32 boards for 5$ that can do way more, have tons of libraries and tutorials online, and those skills are potentially better transferable to other MCUs (from similar series/vendors) down the road. What upsides would it have to use this board, with a potentially unknown architecture, ancient/unknown tools, apart from delaying its e-waste cycle? Especially if its only a handful of boards. If we're talking about 5$, realistically I could only spent 15-20min on that, otherwise I value my time more.

[MathWizard]

Ok so it can be done sometimes. I have an Arduino, and some other similar thing for another chip, and some common MCU's, whatever I try should be with them 1st anyways. Some of my salvaged chips are common, but yeah I guess some are old and obsolete too.

The 16bit TV MCU has internal ram and rom. It has a bunch of 16bit ADC channels. IDK what I'd need those for, maybe some day I'll make a light following robot. I guess I could copy and paste programs for that on Arduino type MCU's.

I played Fallout games too much, and watched too much Terminator movies, in a post-Apocalyptic world, I'd be trying to repair and re-purpose old electronics.

I guess in that future, even if I had electricity, I wouldn't have the internet, and datasheets, or programming guides. So then yeah only the most top level EE/programmers/hackers, would get anywhere with it.