MSX PPI vs 8255

Par Argon

Paragon (1119)

Portrait de Argon

08-09-2020, 16:02

The MSX wiki says the PPI is similar to an 8255 chip.
But how similar are they? Can I just replace a PPI with an 8255?

Also, can an MSX computer boot without the PPI present?

Thanks

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Par lkpalwa

Expert (105)

Portrait de lkpalwa

08-09-2020, 16:22

No! If you are talking MSX engine, that have almost all a PPI then it can't just be replace by a 8255, is only a part of the functions, there is some MSX that do not have engine .. does use a 8255 plus discret logic chips (74lsxx) to make the magic happen, for more details of the PPI and reverse engineering that I am doing look into infodocmsx.com.
Another good source is for example the MSX Data book or the MSX Data PACK 1-3.
(also available in the site or use google to find a PDF copy)
Regards/AW Wink

Par Argon

Paragon (1119)

Portrait de Argon

08-09-2020, 17:22

Thanks!

Par sd_snatcher

Prophet (3482)

Portrait de sd_snatcher

08-09-2020, 22:27

Argon wrote:

The MSX wiki says the PPI is similar to an 8255 chip.
But how similar are they? Can I just replace a PPI with an 8255?

The MSX PPI is a standard Intel i8255 (or compatible). It's not just similar, it's that very chip.

All MSX made with discrete chips will have one.

Later, the PPI was integrated inside the chipset (aka MSX-Engine). Only those specific implementations are optimised to have just the features used by the MSX architecture.

Quote:

Also, can an MSX computer boot without the PPI present?

Only the MSX1 ROM can boot without a PPI. You have to map the ROM to 0000h~7FFFh and the RAM to the 8000h~FFFFh.

Are you planning to build a DIY MSX computer?

Par Argon

Paragon (1119)

Portrait de Argon

09-09-2020, 07:46

No, I'm trying to repair a Philips VG-8010.
I'm not 100% sure what is broken in it, but I think it must be the TMS9129NL or the PPI.

A TMS9129NL is very expensive, so I want to try the 8255 first :-)

K.

Par lkpalwa

Expert (105)

Portrait de lkpalwa

25-09-2020, 14:04

if the are on socket, just take them of an clean legs with some isoproponal and rub them softly with some sandpaper, this are old chips and oxidation can make stuff not get contact with the socket oO

Par sd_snatcher

Prophet (3482)

Portrait de sd_snatcher

25-09-2020, 21:44

Argon wrote:

No, I'm trying to repair a Philips VG-8010.
I'm not 100% sure what is broken in it, but I think it must be the TMS9129NL or the PPI.

What are its symptoms?