65C02 computer with composite video generation

[DPax92]

GARTHWILSON wrote:

There should be about a turn and a half of insulated wire wrapped on the post.

Thank you for the suggestion, I read it from the WW primer (which really is a magnificent reference, thank you!), but I struggled to achieve it. I realized that my technique was wrong, but after some more practice I managed to get better wrappings. Are the ones shown below more correct?

Dr Jefyll wrote:

What I do myself is begin with the bypass capacitors.

That would have been indeed a better idea. Initially, I thought about leaving two additional pins on each socket and then solder the bypass capacitor there. Would the wire be too long? I still can solder the capacitors on the other side of the board, I have sufficient space below the ICs.

Regarding the wiring pencil, it seems to be very interesting. However, I like the fact that very little soldering is needed for Wire Wrapping, because I live in a very small flat and I have no dedicated work bench, so I prefer to keep the soldering iron cold


Regarding the project, I have been working this weekend and finally I'm getting faster at wire wrapping. I have also started to test the work done up to now. In the picture below you can see the wiring done up to now, as well as my testing setup. On the upper part of it you can see my simple EEPROM programmer that I use with Arduino. I also taped a breadboard to the main board and I installed a set of LEDs to shown the address and data busses, for debugging. Right now, I'm testing the connections by forcing the data bus to $EA (the blue wires), reading the address bus of the ROM socket. All seems to be working correctly and the CPU is "running in circles", which gives me convidence to proceed.

Regarding bypass capacitors, do all ICs require one? Or better said, should I put one for each IC? I was wondering if the stack of 4 address multiplexer could operate with a single capacitor.

Thank you for your kind help!

Regards,
Davide

[GARTHWILSON]

It's looking pretty good. If the corners of the posts are sharp, there's no need to solder. The connection will never fail.

Capacitors can also be soldered onto the tops of the ICs. In most cases it will mean taking the capacitor's leads across the corners of the IC, as directly as possible, with the leads and the capacitor right against the top of the IC package.

[BigDumbDinosaur]

GARTHWILSON wrote:

It's looking pretty good. If the corners of the posts are sharp, there's no need to solder. The connection will never fail.

However, beware of the negative effect skin oils can have on connections. Avoid touching the area of the post to which the wire will be wrapped. Cleaning it with a cotton swab dipped in some isopropanol or acetone (but not saturated) will remove all traces of skin oils.

[GARTHWILSON]

BigDumbDinosaur wrote:

GARTHWILSON wrote:

It's looking pretty good. If the corners of the posts are sharp, there's no need to solder. The connection will never fail.

However, beware of the negative effect skin oils can have on connections. Avoid touching the area of the post to which the wire will be wrapped. Cleaning it with a cotton swab dipped in some isopropanol or acetone (but not saturated) will remove all traces of skin oils.

Yes, and contamination is addressed in the "Answering Wire-Wrap (WW) Questions and Doubts" page of the 6502 primer, linked above. Cleanliness is one of the reasons I do not buy pre-cut and -stripped WW wire. You should wrap it soon after stripping, and avoid touching the wire with your fingers. I avoid touching the pins with my fingers too, except for at the points. It's not difficult to handle the sockets while avoiding touching the sides of the pins.

[DPax92]

GARTHWILSON wrote:

If the corners of the posts are sharp, there's no need to solder.

I do not understand, do you suggest to wrap the leads of the bypass capacitors directly to the WW posts?

Regarding the problem of skin oils, I follow the "mitts off!" rule of the primer, and strip the wires right before wrapping them

Regarding bypass capacitors, I understand that the suggested value is 0.1uF. Which type of capacitors should I use? I understand that ceramic caps are usally employed but I have a bunch of polyester ones readily available.

Thank you for your help!

Regards,
Davide

[BigDumbDinosaur]

DPax92 wrote:

GARTHWILSON wrote:

Regarding bypass capacitors, I understand that the suggested value is 0.1uF. Which type of capacitors should I use? I understand that ceramic caps are usally employed but I have a bunch of polyester ones readily available.

I use 0.1 µF, 50 V, X7R MLCCs in my projects.

[GARTHWILSON]

DPax92 wrote:

GARTHWILSON wrote:

If the corners of the posts are sharp, there's no need to solder.

I do not understand, do you suggest to wrap the leads of the bypass capacitors directly to the WW posts?

No, I guess I missed that. The capacitor leads will be too fat to go in the WW tool. When you solder them, make sure you use a minimum of solder and keep the solder off the rest of the post, so that it won't effectively round out the post and make the corners less able to bite into the WW wire that will be added later.

Quote:

Regarding bypass capacitors, I understand that the suggested value is 0.1uF. Which type of capacitors should I use? I understand that ceramic caps are usually employed but I have a bunch of polyester ones readily available.

You want the lowest possible equivalent series inductance. Multilayer ceramic capacitors are good for this. I don't know if the polyester ones are inductively wound. You could see if there's information on them from the manufacturer. I think you'll find that they're intended for audio and not digital or RF.

[DPax92]

Thank you very much both of you, I will get some ceramic capacitors then!

Out of curiosity, what is the effect of skin oil? Does it immediately cause bad conductivity or does it cause long term corrosion?
I realized that I may have touched some wires, to straighten them for example, before wrapping them. Is the damage done or can I do something about it?

Thank you very much!
Davide

[GARTHWILSON]

The wire and pin need to be clean and free from skin oil in order to get a good chemical weld as you do the wire-wrapping. When you need to straighten the wire, pull it through tweezers or something like that.

[DPax92]

GARTHWILSON wrote:

The wire and pin need to be clean and free from skin oil in order to get a good chemical weld as you do the wire-wrapping. When you need to straighten the wire, pull it through tweezers or something like that.

Thank you, so should I do something about the connections I have already made or just be careful for the future ones?

Davide

[Dr Jefyll]

I would say just be careful for the future ones. And (something obvious, but not yet mentioned), try to keep your hands clean while you're working. Wash them before you start, and be willing to wash them again periodically -- especially after touching your face, or pausing to eat your lunch, etc.

Remember, BTW, that you have the option of soldering any connections that give trouble. I understand you're reluctant to do that, but there may come a time when it becomes the best option.

-- Jeff

[GARTHWILSON]

The ones already touched and wrapped may be fine. There's a small risk, but that's all it is—a minor risk. It compounds as the number of such connections increases of course. You might want to keep a note of which ones you did that way, then just keep cleaner from now on. Like Jeff says, you can solder them if you have a problem and troubleshoot it and find that that's the cause. If you solder it though, you can't unwrap it later if you want to make modifications.

I have always been very careful, and I have never—not once—had a wrap fail; and I'm regularly using ones I did nearly 30 years ago. OTOH, I have a friend who, in engineering school in 1983, used WW for his senior project. He worked on it late into the night the night before he was supposed to demonstrate it. He took it in, demonstrated it, and it worked for that short time, but no longer worked when he got it back home. He traced the problem down to his poor wire-wrapping.

[DPax92]

Hello everyone!

I've been away from the project for almost two months because of my job, but now I'm back at it. I've been busy during the Easter holidays however. I've made an enclosure for the computer using an old satellite tv receiver, and I've painted it a nice shade of blue Also, I've built a more "robust" version of my Arduino EEPROM programmer on a breadboard with soldered wires.

Regarding the computer, I've added the VIA, and I've connected it to an Arduino Micro which generates the USB signals to connect to my modern computer. In my first breadboard computer I used the 6522's shift register, because the Arduino was generating the clock signal and I could avoid the notorious serial bug. This time I've decided to use PORT A and go with a parallel connection. I've got pins to spare on the Arduino and also other 4 6522s in my shelf, so I decided to be lazy and also get a bit of more speed
I've adapted the code I wrote for my first project to get serial IO. As of now, I've implemented 4 commands: Memory page dump, memory byte setting, program loading from serial, and program execution. Now, I'm planning to implement code to flash the ROM contents directly via serial so that I do not need to physically remove the chip from the computer. When that is done, I will proceed with the video generation circuit.

Thank you all again for your help!

Davide

[DPax92]

Dr Jefyll wrote:

I would say just be careful for the future ones. And (something obvious, but not yet mentioned), try to keep your hands clean while you're working. Wash them before you start, and be willing to wash them again periodically -- especially after touching your face, or pausing to eat your lunch, etc.

Remember, BTW, that you have the option of soldering any connections that give trouble. I understand you're reluctant to do that, but there may come a time when it becomes the best option.

Sorry for my late reply! Thank you, I'll consider soldering should any connection give me trouble. That is not really an issue, I would just try to keep it to a minimum Regarding clean hands, I've tried latex gloves (actually, only one glove on the right hand) and I find it quite useful, so that I can touch the wires to straighten them should they get bent while stripping etc. Have you ever used them?

GARTHWILSON wrote:

The ones already touched and wrapped may be fine. There's a small risk, but that's all it is—a minor risk. It compounds as the number of such connections increases of course. You might want to keep a note of which ones you did that way, then just keep cleaner from now on. Like Jeff says, you can solder them if you have a problem and troubleshoot it and find that that's the cause. If you solder it though, you can't unwrap it later if you want to make modifications.

I have always been very careful, and I have never—not once—had a wrap fail; and I'm regularly using ones I did nearly 30 years ago. OTOH, I have a friend who, in engineering school in 1983, used WW for his senior project. He worked on it late into the night the night before he was supposed to demonstrate it. He took it in, demonstrated it, and it worked for that short time, but no longer worked when he got it back home. He traced the problem down to his poor wire-wrapping.

Sorry too for my late reply. I have kept a small list of the components which have "dirty" connections so that I will know to check continuity should they give me trouble, thank you for the suggestion!


Kind regards,
Davide

[GARTHWILSON]

DPax92 wrote:

Regarding clean hands, I've tried latex gloves (actually, only one glove on the right hand) and I find it quite useful, so that I can touch the wires to straighten them should they get bent while stripping etc. Have you ever used them?

If they need straightening, I pull them through tweezers, again without touching the bare wire with my hands. This also goes for those few times I need to re-wrap, like if I realize I wrapped the wire onto the wrong pin, or I did it poorly. I use the unwraping end of the tool to remove it, straighten the wire back out, and try again. This is covered in the WW chapter of the 6502 primer.