Amstrad PPC512 & PPC640 3 slots ISA Expansion Card V2.1

This project consists on an minimalistic expansion card with 3 ISA slots for the Amstrad PPC512 and Amstrad PPC640 "portable" computers from 1988. These computers are based on the NEC V30 (8086 compatible) with either 512KB or 640KB of RAM respectively and they expose all the signals of the standard ISA slots on two D-sub connectors on their backs.

I started working on this project back in 2016 but it has been dormant until January 22, 2021. On this day I noticed a Youtube video by Noel Llopis regarding PPC512 upgrades [1] and that triggered something in me to get this project finished.

This page now features an updated version of the PPC 640 ISA expansion card (blue PCB / v2.1), developed between April and May 2022. If you're looking for the original one (green PCB / v1.0 issue 2), click here..

Schematic

Following the instructions on the Amstrad PPC technical/reference manual:

Address lines A0..A7 from the PPC D-sub are buffered with a 74HC244
OSC, MEMR, IOR, ALE, CK4, MEMW, IOW, RESET from the PPC D-sub are also buffered with a 74HC244
All data bits D0..D7 from the PPC D-sub are pulled up with 10K resistors

Contrary to the instructions of the reference manual, I decided not to power the PPC using the expansion ports and do the opposite: let the PPC power the expansion card.

Since I will only be using low power cards like a XT-CF card to add a "hard disk" and maybe a VGA card (which I still have to find), they will be powered by the PPC, ie, parasitically.

Bugfixes on PCB v2.1 (blue)

Removed connection from pin B20 to +12V as this disables the PPC's internal switching regulator and thus prevents the computer from working.
Enlarged most of the tracks carrying supply voltages and ground.
100nF capacitors now have the correct 2 pin package
Minor silkscreen text changes

Parts (BOM)

Not many parts are required to make this expansion card.

ID	Part
X1	25 pin D-Sub Male for cable
X2	37 pin D-Sub Male for cable
C1, C2	100nF/50V 0.1" capacitor
C3, C4, C5, C6, C7, C8	10uF/25V capacitor
IC1, IC2	74HC244 + DIP20 socket
RN1	SIL 10K * 8 resistor pack
X3, X4, X5	62 pin ISA socket
H1, H2, H3, H4	Mouting holes. I'm using 30mm long screws and nuts to support the weight of the expansion card plus other ISA cards

PCB

Version 2.1 of the PCB basically fixes problems found on the original one and assembling it should be pretty straightforward.

Both D-sub connectors are soldered directly to the PCB edge and the PCB itself should be supported by four screws set to the height required to level the PCB and also mechanically support the expansion cards.

The cards should have their ICs facing the PPC with their metallic blades to the right side (where it reads READ SIDE), when looking to the computer from the user perspective.

Here's a view of the expansion D-sub connectors on the back of the computer, right beside the power input jack.

Prototype

Like the original one, this new PCB also took a while to arrive from China. I got them at the beginning of May and quickly assembled one with the minimum number of parts, and connected it to the PPC. And I can say everything worked perfectly the first time. There are currently no identifiable problems with the card.

Pictures and Videos

The card being assembled and first tests

Testing it with a XT-CF card (features the new v2.1 expansion card)

Booting from a Compact Flash card (legacy video from the original V1 expansion card)

Intro tune of Space Race (legacy video from the original V1 expansion card)

The ISA Expansion Card out there

This ISA expansion card has been featured out there on the internet, most notably on the North Devon Retro Computing Archive website and on several YouTube channels.