6502.org

That varies between manufacturers, so check the data sheet. IIRC, Rockwell 'C02s and all NMOS 6502s accept TTL levels on their inputs -- so 3V would be acceptable as a logic high. But, contrasting with that, WDC 'C02s place the input transition around 50% of VCC. With the chip running on 5V, a 3V input signal would be too close to 50% to be a reliabe logic high. (You could consider running the chip at 3V, though.)

Best to check, as I say.

It's been a while, nothing but problems with all my projects. Half the chips I bought don't work, the replica 1 video section is starting to get finicky, and my nvram circuit didn't work at all. Lots of fun.

In a desperate attempt to do something enjoyable again, I've started drawing up schematics and layouts for the pulsar computer. I have a quick question about the intel p2102a memories, I can't find much info on them online besides basic specs. How do you use the separated data bus? Is it alright to connect Din and Dout directly together to the system bus, or do they have to go through a couple of tri drivers? Both ways?


Also, does anyone either know where to get chips relatively cheaply, or are interested in selling some used spares? Jameco is going to end up close to $15 for a single mpu between minimum order and shipping, which isn't practical for me. Most of the chips on ebay are from China, and of shady origins.
I need:
W65C02S
28C64 (or other eeprom)
65(C)22
65(C)51

Thanks!

Who/what are you using for your chip source(s)?
In the USA, it's going to be Mouser or Jameco for genuine WDC parts. You can't avoid the cost of shipping, and as someone whose company does business with both, I can tell you that shipping from Mouser is cheaper than from Jameco. I don't have any ironclad proof, but I have a suspicion that Jameco marks up what UPS charges them and thus ekes out some profit from shipping. Mouser passes through shipping without markup and also offers more options in that regard. The only items I purchase from Jameco are ones that are not available from stock through other sources.
You're just now discovering this?

As I recently wrote on another topic, <quote> from time to time someone on the forum is sure the new parts they just got are dead. I have never had defective ICs from a supplier. Never. I started buying ICs in 1975 in my hobby, and 1985 in my work. You do of course have to be careful about static handling precautions, and I see people get pretty careless about that. Make sure you're going by the data sheet, and then make some measurements before putting the new part in the socket. Check power & ground first, then feed it the intended signals and make sure they show up at the socket pins correctly, etc..<end-quote>

It would be helpful if you could post your schematics. Make sure you observe the considerations in the 6502 primer.
Where are you, like what country or state?

He's in South Carolina, Garth. I recommend he order through Mouser.

What I can from my collection, all of which are old and most of which seem to work as expected. For the more specific parts, I did buy from ebay. Mistake I guess, but less than half the price was hard to resist. So far the only chip that seems to sort of be working is a 65c02. So they aren't just plastic, but I don't know what's wrong with them.

I can write up schematics if I need to, but the main one was the eeprom. My little programmer works fine with any RAM I put in it, and the ROM's control lines seem to be working, but it won't write. I'm using a known working circuit (mentioned above), and have triple checked all the connections.

For the 6522, I connected all the data and control lines, and put it on the $c000 block of the replica 1. I sent $ff to $C002,3 and $AA to $C000,1. LEDs on the ports are dimly lit before running the program, and after pa0 is lit and the rest are dimly lit. Seems broken to me, but I don't know much about the chip. I'm just following a tutorial.

The nvram circuit just involved a cr2032 battery and two diodes on top of a ram chip, with a 10k resistor holding /ce high. The datasheet shows data retention down to 2v (diode/battery supplies 2.6v), and power consumption of microamps. Problem is, the data corrupts at anything less than 4.5v. That's annoying, but I do understand to some extent what is wrong. Very slightly different chip numbering could be a problem.
Yes. It seemed to me if that's where many come from anyway, buying from a seller with good feedback couldn't be that big a deal. Oh well.

Yes Garth, I'm in SC.

I'll look into Mouser, thanks for the suggestion.