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Good morning and welcome back to the ValorosoIT channel: the channel dedicated to vintage computers and electronics! Today we try again to expand the RAM of this beautiful Commodore PC10. If you remember, I posted a short video where I tried to expand the RAM, but I wasn't successful. Many of you had tried to help me, but the person who really succeeded was Nicola Avanzi, whom I thank publicly. Among other things, it is not the first time that I have thanked Nicola Avanzi within the ValorosoIT channel, because a couple of times he had already given me some nice objects, such as an expansion that applies to the User Port of the Commodore 64 and some programmers. Nicola Avanzi confirmed what was one of my doubts, that is, the fact of having to upgrade a chip (a PAL - therefore a programmable logic) inside the computer, because it did not manage 640 KB of RAM, instead of the original 256 KB of the computer. Well, today let's do this test: let's see if, in fact, we will be able to expand the computer's memory.
I've wanted a Commodore PC-10 in my collection for a long time. First of all because it is Commodore, therefore a brand I am very fond of. Secondly because it is an IBM compatible computer, so it is a PC. It is from 1984, has an Intel 8088 processor, 256 KB of RAM. But, given that I want to run Fortnite on it (!!!), 256 KB seems a bit small to me. So I decided to expand it to 640KB of RAM. It has no hard disk and has two 5 1/4 inch floppy disk drives, disk A and disk B.
As you know, on my website www.valoroso.it, I publish the computer cards that I have in my collection, unfortunately I can't manage all of them, but I have published them for this Commodore PC10. Inside you will find the features of the computer. Ah, I ask you every time, since many of you who watch my videos are not subscribed to the channel, subscribe to the channel and activate the notification bell. It doesn't cost you anything, but it gives me a lot of pleasure.
Now, I'll save you the mechanical maneuvers of opening the computer: I'll open everything myself and make the motherboard available to carry out the operations needed to expand the RAM. It didn't take me long, the computer is here, disassembled, now I'll show it to you. So, first of all I removed the upper part of the case, then I removed the two floppy disk drives, which I placed there. It's very simple to do this: there are two screws on this side for each floppy and one screw on the other side. Then I also removed the power supply, with the four screws that hold it to the back of the case. At this point you can see the inside of the computer. You see that the motherboard of my computer model is split into two parts (assy 380900-01 rev D), because I know that there are Commodore PC10s with whole motherboards, not split into two parts.
I had to do some testing on this computer, so I already had a diagnostic card installed for the ISA bus. This is the video card, but now I'll also show you the other video card that came with the computer, which was this one: always an 8-bit ISA video card. I don't know why this computer had two video cards. Furthermore, in the manual, therefore both in the User Manual and in the Service Manual, only this tab is indicated here, not this other one, which I therefore temporarily removed. But it works: I tried it and it works.
Let's proceed. At this point I install the two banks of RAM chips. These are RAM chips that I salvaged (temporarily) from a working computer. I had already done this, you also saw it in the short video. In fact I wrapped up later. Now we are going through all the steps again and let's see if it works differently this time. They are RAM compatible with those already present. So, these original ones here are MB81256, 256 Kbit, for 1 bit. In practice, to form the byte you need 8 chips and therefore each will form a bit of the single byte and in addition there is the last chip which is the parity, which is a control of the value of the RAM cell.
We install the chips. For each RAM bank, nine chips must be inserted, in total we should add 18 chips. You need to follow the correct orientation. So, the TMS4256 chip which, obviously, as I said, was already compatible with the existing memory, has a reference cleat that needs to face this side and you can also see on the sockets that they have a reference cleat.
I moved to the second bank of RAM chips. So, in theory, I had done the first experiment only with the first bank of additional RAM and I would have also been satisfied with having 256 KB more, because it already has 256 KB. With 256 KB more we arrived at... - so, I can't talk while I do the work, eh, so if you see me hindered with the chips, it's because in the meantime I'm also talking and recording! -
So, I was saying, we could only do the first bank and get to 512 KB or also add the second bank of RAM, another 256 KB, which however the computer doesn't read all of which and we get to 640K in total, at least on paper. This, in theory!
The chips are all inserted, all 18. At this point, the Service Manual indicates the positions of the DIP switches to use. So now I have 640 KB of RAM. We can see that switches number 3 and 4 should both be off. The switches are here. Currently 1 is off, 2 is on. Which corresponds to, let's say, the 1 BOOT, so it means that the computer can start, it is not in diagnostics. The 2 on corresponds to the Intel 8087 math coprocessor not being installed. Now let's look at 3 and 4. 3 and 4 are currently: off and on. Off and on corresponds to 256 KB. Now we turn them both off, then up, to get to 640 KB.
Ok, done. Then the other four switches are for the video card, therefore the type of video card installed and the number of disk drives installed. At this point, I thought that the RAM was installed and properly configured, because on any other computer that I had ever done in the past, that I had ever expanded the RAM, this was the operation that had to be done.
In fact, turning on the computer, I would have imagined seeing the RAM count here which went up to 640 KB, but no!
Do you see? The count stops at 256 KB. Okay, now it also gives the error to disk drive A because obviously I removed them.
And this is where Nicola Avanzi stepped in with his suggestions. In fact, some have suggested to me: But look, maybe the RAM chips are wrong, maybe there are some that don't work.
In reality, I thought that this wasn't possible, because otherwise the computer would have identified them, but it would also have given an error. I also thought it was the BIOS, I don't know if you want to pronounce it the Italian way or the English way. I had updated it... In short, we're always talking about 40 years ago. Let's say I updated it to version 2.05 compared to 2.03, but nothing had changed. Additionally, I had also tried programming BIOS replacement EPROMs with diagnostics and they also did not identify the additional RAM.
The culprit was this chip here, a PAL (or PLA): programmable logic. And, as was suggested to me by Nicola Avanzi, I purchased a GAL 16V8D, which is also programmable logic compatible with the original PAL 16L8. Only, a little more recent. I programmed it with the programmer I usually use: the TL866II Plus. So, the programmer supports a lot of EPROMs and also GAL (generic array logic). The ones I purchased are the GAL 16V8D from Lattice. I don't know if it's pronounced Lattice or who knows how else... and in any case it's a name that's not very suitable for the ValorosoIT channel.
You load the JED programming file, which Nicola Avanzi kindly provided me and you go to GAL programming. This programmer is truly a godsend, it costs very little and truly programs everything. Here, it says that the programming was successful, so we can remove the chip from the programmer and try to install it in the computer. Let's see if Nicola Avanzi is right, and I sincerely hope so, because... otherwise I will never be able to play Fortnite with my Commodore PC10.
Here it is. This is the original Commodore chip. Then they explained to me that this fact of having to replace a chip programmed with Commodore software inside - a programmable logic - was desired because it discouraged people from wanting to do the RAM expansion work themselves, because otherwise one would have bought the 256 KB computer and would have expanded the RAM themselves, saving money. Not having the source code present within this PAL, where I have now placed a GAL, we would not have been able to carry out the operation. Instead, thanks to Nicola Avanzi, I was able to do it. Now let's cross our fingers and hope that it really is the right time. This is the original, old PAL, we keep it aside and this is the new GAL. Furthermore, the new GAL is also reprogrammable, so now I use it to do this work, but it is not certain that in the future I will be able to delete it and reprogram it for some other chip which obviously must be pin to pin compatible. Let's hope... fingers crossed... Shall we turn it on?
Let's see... 256... Yes, he's counting!!! Yes... No, it went back... No, but it's going... it's going... this time it saw it, the RAM saw it!!!
We did it!
Ok, the RAM expansion was successful!
So, now I'll reassemble a floppy disk drive and try to load DOS and a little game.
Here... Fortnite no, eh, I was just saying it. It's not like I can try to load it... Load... Arkanoid, come on.
Here it is, the floppy connected in a slightly temporary way. We put the disk inside, turn it on in the correct order, so first the monitor, then the computer, as I was always taught to do. So, every now and then, but it's not the floppy's fault, this computer gets stuck and that's why I put in that diagnostic card. In fact, if any of you help me on this problem too, I'll avoid removing all the chips one at a time and trying them. In practice, what happens? It gives Reset, but then Ready doesn't come out and therefore the computer doesn't start.
This thing happens every now and then and honestly I haven't looked into it in depth yet, but it will be a topic for other videos. Ok, I reboot, then turn it off and on again until the computer starts. In fact, now you see that he has left. Then he gave the Ready signal and starts counting.
Wow! What a beauty to see this RAM up to 640K! Who knows what I can do with 640Kbytes of RAM...
It is loading MS-DOS.
Sure enough, there you have it, he uploaded it. Now let's remove the DOS disk and put the Arkanoid game disk on it.
He's leaving. CGA. The Keyboard with the K. So, the monitor also does this every time. Behind there is a trimmer to adjust. Now, since I have my cell phone in my hand, I can't do it live. I pause the video for a second and then start again. Yes, very convenient, eh, that every time the resolution changes one has to adjust the trimmer, but... that's how it is.
Yes, yes, come on. Let's play, let's play. What are the keys? Ah, ok, these two here and then with space we disappear.
So, with one hand I hold my cell phone, with the other I try to play. It's not exactly comfortable, eh. Then again, I'm already rubbish at video games, plus I seek out difficulties on my own. Now the computer is playing itself and is better than when I play.
So, we expanded the RAM to 640 KB from the original 256. There were basically three steps: one, installation of the RAM chips on the two banks that were empty. Not all the mainboards of these computers have empty banks, eh. This one had empty desks and therefore this operation can be done. Two, the DIP switches to be set according to the correct size of the RAM. And number three, the replacement of the PAL, of the programmable logic, with a GAL, which is the modern equivalent - modern, anyway, already out of production for who knows how many thousand years, eh - with the program such that the computer can also recognize the additional RAM. Thanks again to Nicola Avanzi. Please, subscribe to the channel if you haven't already done so and I'll see you in the next video... on the @ValorosoIT channel.
Ciao!