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Recording request: NEC µPD7756C and the Mitsubishi M50805
http://forums.nesdev.com/viewtopic.php?f=6&t=16129
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Author:  seanriddle [ Tue Jul 04, 2017 4:31 pm ]
Post subject:  Re: Recording request: NEC µPD7756C and the Mitsubishi M5080

I found another Aerobics cart for $12, so I bought it and decapped the chip in the one B00daW sent me: http://seanriddledecap.blogspot.com/201 ... -post.html

The 312-byte decoding ROM is easy to spot, but unfortunately the 960-byte parameter ROM seems to be implant ROM, so I can't see any of the bits.

Author:  seanriddle [ Thu Jul 06, 2017 12:46 pm ]
Post subject:  Re: Recording request: NEC µPD7756C and the Mitsubishi M5080

I needed a primer on PARCOR/LPC, and Cater's Electronically Speaking has a good introduction: http://www.seanriddle.com/lpc.pdf

As Lord Nightmare said, this looks a lot like TI's LPC.

Author:  B00daW [ Thu Jul 06, 2017 1:40 pm ]
Post subject:  Re: Recording request: NEC µPD7756C and the Mitsubishi M5080

So the decoder ROM is in the middle left and the parameter ROM is on top?

Author:  seanriddle [ Thu Jul 06, 2017 3:40 pm ]
Post subject:  Re: Recording request: NEC µPD7756C and the Mitsubishi M5080

Yep. The decoding ROM bits are easy to discern, although I haven't tried figuring out the layout. I can't see any bits in the parameter ROM.

The top left pad is pin 4, numbered counter-clockwise. It's easy to spot the power inputs and the huge drivers on DA0 and DA1. The 2 pads in the lower right aren't connected to anything. There's an extra pad, so I assume the 22-pin and 24-pin versions use the same die, but clock output isn't pinned out in the 22-pin version.

I put more info here: www.seanriddle.com/m50805.html

Author:  Lord Nightmare [ Fri Jul 07, 2017 2:55 pm ]
Post subject:  Re: Recording request: NEC µPD7756C and the Mitsubishi M5080

sean, can you take a hi-res image of the smaller, visible rom area? I should be able to get the lpc tables extracted, but I need more zoom.

LN

Author:  seanriddle [ Fri Jul 07, 2017 3:58 pm ]
Post subject:  Re: Recording request: NEC µPD7756C and the Mitsubishi M5080

Here's the decoding ROM at 3Kx4K pixels: http://www.seanriddle.com/m50805metaldecodingrom.jpg

And I uploaded a 32Kx32K pixel full die shot to WikiMedia: https://commons.wikimedia.org/wiki/File ... tal20x.jpg

Author:  seanriddle [ Sat Jul 08, 2017 1:58 am ]
Post subject:  Re: Recording request: NEC µPD7756C and the Mitsubishi M5080

And here's the decoding ROM with the top metal removed: http://www.seanriddle.com/m50805aciddecodingrom.jpg

Author:  B00daW [ Sun Jul 09, 2017 5:52 pm ]
Post subject:  Re: Recording request: NEC µPD7756C and the Mitsubishi M5080

So looks like we could read the decoder ROM to assemble a binary from it... What do you think the next logical steps for the parameter ROM should be? Lord Nightmare?

Author:  Lord Nightmare [ Tue Jul 11, 2017 1:38 pm ]
Post subject:  Re: Recording request: NEC µPD7756C and the Mitsubishi M5080

The 960 byte rom may require etch/staining, which is outside my realm of expertise :(
However it is likely we have the entire contents of it anyway from the data line traces?

LN

Author:  B00daW [ Sun Sep 10, 2017 3:42 pm ]
Post subject:  Re: Recording request: NEC µPD7756C and the Mitsubishi M5080

Is there any program made that can analyze a decap picture through filters and bitmap (with proper image setup and formatting) to create a dump?

I'm not sure what I'm looking at regarding which is a 0 and which is a 1 regarding the decoding ROM decap...

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