Amstrad PPC640: Part 2 (internal RAM layout & internal ISA plans)

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The Clueless Engineer

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Published on August 6, 2023 11:06:59 PM ● Video Link: https://www.youtube.com/watch?v=s2bv70iCfGo

Duration: 12:52

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A quick look at the internal layout of the Amstrad PPC machines. It would make sense that the PPC512 and PPC640 shared all the same internals, just 128KB less RAM on the PPC512 board.

There is a LK4 on the board that tells the system how much RAM is installed.

In the PPC640 the installed RAM comprises (all 150ns or better):

18 x M41256A-12 (120ns, eight per 256KB bank, one parity per bank)
4 x MT4067-10 (100ns, two per 64KB bank)
2 x KM4164B-15 (150ns, one parity per 64KB bank)

There is one parity bit per one byte of RAM ... so actually nine bits are stored for each byte.

I guess, to upgrade a PPC512, you'd need four 64K x 4bit and two 64K x 1bit ... ?

Interestingly (to me, at least) the machine uses a Sony copy of the NEC V30 instead of an 8086: the snappily named Sony CXQ70116P-8. There is space for an 8087 maths co-processor beside it.

The V30 is supposedly 10-30% faster than an otherwise equivalent 8086.

I've started building the simple external ISA expansion board - E14 has the ISA edge connectors out-of-stock until September ... but I want to try a right-angle one (pricey) for the internal install ...

External ISA expansion board for Amstrad PPC:
http://www.enide.net/webcms/index.php?page=ppc512-640-isa-expansion

My other videos about the Amstrad PPC:
https://www.youtube.com/playlist?list=PL5pwokf56wMKMBxEwF7Jkr8V6Q7_fJ6iU