PPC MLDL

[_dev-null]

Hello!
Is someone out there who build the PPC MLDL and got it working?
I build it over the last days and failed. I try to get the PROMO* signal at the right time to the EPROM ... but it doesnt work.
Maybe there is a fault in the Phase Counter, but i checked it over and over again as well as all other parts.
I think I have to dig out my Logic Analyzer ...

Anybody had a similar problem?

Here are some pictures: http://www.sp-net.at/nextcloud/apps/gall...4PQx9nqSBQ

Regards
Stefan

[MeindertKuipers]

This is an ambitious project, lots of respect for the fine wire soldering!
The PPC design for the MLDL is not perfect, but close and should give some results. Make sure that you decouple the IC's.
I have built my own MLDL with the Eramco kit, and that largely follows the same principle as the PPC version. But that did not work immediately. I am currently working to reverse engineer it (create schematics from the hardware), but without at least a scope you will not be able to get it working. I remember from the Eramco MLDL that it worked suddenly when probed with a scope at some point (I put a small cap on that pin), so there is probably a critical timing condition.
First thing to check is if the timing generator creates the pulse at the right momen, and the power circuit to the Eproms is a bit tricky, some Eproms may need some time to startup.
Good luck!

[hth]

I never heard of the PPC MLDL.

Back in the days I wired my own based on the design in a PPC Journal (Lynn Wilkins I believe).

I changed the design a bit to use a single 8K EPROM and read out 2 bits and latch, then read out the lower 8 bits. That gave me a single EPROM per 4K module (not the 4K + 2K variant). I also powered up the chip one cycle earlier with the hope it would ramp up power for working with my 2x speeded 41CV and it did.

The only problem I had was that it did not work first. A scope helped me show the problem. One of the signals had its spikes but also a tiny thin spike. That was the counter for 30. After some thinking I realized that when it wrapped from 39 to 40, it very briefly had 30 again, screwing everything up. The 10 and 1 counters are separate. I added one extra AND gate to only check that signal in the "middle", which sorted the problem.

I used wire wrap wire, but soldered directly on the chip legs, no sockets. That MLDL has a lot of wiring, supported 2 RAM pages and 4 EPROM pages. I used it for years without any problems and it probably still works. Power mileage was good too.

I bit-banged a serial port connected to the MLDL to download software to its RAM by simulating the 41 bus. The computer had one cable, the 41 one and the MLDL had a very nice quick release connector.

These days I use a simulator for most development, MLDL2000 for early testing and Clonix for production.

[_dev-null]

Hello!
I got it working!!! It turns out that the transistor, that turns VPS on for the EPROMs was faulty. Such a small thing and so much trouble ...
Now it is time to wire the RAM and I/O Ports. I will post more pictures of my work tomorrow.

Stefan


PS:
With "PPC MLDL" I mean the MLDL that is described in the PPC Journal V9N3.

[_dev-null]

Hello!
My MLDL is now fully assembled.
The EPROM Part of the MLDL works perfect. The RAM (called "ROME" for ROM Experimental) is not fully tested and needs a backup battery.
I also need to test the I/O ports, but a FFFF000 send to the MLDL generates a pulse at WPORT* so i think it the output port works.

Currently i have X>ROM and ROM>X loaded on the EPROMs, and the CCD Rom, PPC Melbourne Rom on the Clonix Module. Maybe i should load the David Assembler also ..

Stefan


Pictures: http://www.sp-net.at/nextcloud/apps/gall...4PQx9nqSBQ

[HP-Collection]

So save time and erros I suggest designing a PBC board with a free available software and "printing" it with a low cost service, instead of using hundrets of meters of wires.....

But also my respect for your work!

[_dev-null]

(03-11-2019 11:16 AM)HP-Collection Wrote:  So save time and erros I suggest designing a PBC board with a free available software and "printing" it with a low cost service, instead of using hundrets of meters of wires.....

No, PCBs are boring I love my wires...
Short update: The RAM works as it supposed to be. I loaded the ML-ROM into the EPROM. Together with the CCD and David Assembler it is a great development environment.
Now i need to build a backup battery for the RAM. Maybe with a Supercap or a lithium cell.

Stefan