M68EC020 vs M68020 ?

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legacy
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M68EC020 vs M68020 ?

Postby legacy » Sat May 26, 2018 10:55 am

The M68EC020 processor has been used as the base processor in some Amiga models most notably the A1200, and the primary difference between the MC68EC020 and the MC68020 is that it has a 24bit address bus.

Here I happen to have a board with an MC68EC020RC20 on the top of the socked, and I replace it with an MC68020RC25 the board doesn't start.

Everything is tested and known of being working, e.g. the MC68020RC25 works for another board.

The starting address is below the 24bit address space, it's located at 0x0080.0000, as well as the stack is located at 0x0000.1000

What could be wrong?
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frank.lukas
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Re: M68EC020 vs M68020 ?

Postby frank.lukas » Sat May 26, 2018 11:03 am

There is a DMA Signal missing on the EC020, see the Datasheet.

EC020.jpg
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Re: M68EC020 vs M68020 ?

Postby czietz » Sat May 26, 2018 11:34 am

As far as I know, the pinouts aren't compatible. Check the datasheet.

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Re: M68EC020 vs M68020 ?

Postby legacy » Sat May 26, 2018 12:29 pm

frank.lukas wrote:There is a DMA Signal missing on the EC020, see the Datasheet.


The board doesn't use the DMA. It bootstraps, it loads the interrupt vector tables, and then it enters into a "monitor" loop waiting for commands from the user-serial line.

I have to check the UM deeply.
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Re: M68EC020 vs M68020 ?

Postby czietz » Sat May 26, 2018 12:37 pm

Even though they both come in a 13x13 PGA package, they're not pin compatible.

68020:
68020.png


68EC020:
68ec020.png


Considering that even Vcc and GND are different, if you're unlucky you have now fried the 68020.
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Re: M68EC020 vs M68020 ?

Postby legacy » Sat May 26, 2018 1:00 pm

czietz wrote:Considering that even Vcc and GND are different if you're unlucky you have now fried the 68020.


Not fried, the chip is still alive and passes all the diagnostics. I put a current limiter on the CPU board.
Anyway, what a stupid design of the package by Motorola, and the documentation of the Socket was not telling about the different pinout :roll:

Lesson learned: you must always check the datasheet!
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Re: M68EC020 vs M68020 ?

Postby legacy » Sat May 26, 2018 1:30 pm

Do you happen to know *where* I can find an adaptor 68020-PGA to 68EC020 PGA?
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