To pull-up or not to pull-up, this is the question..

[walter.preuninger]

Happy New Year Everyone!

Over my 3 days off, I threw down a WDC6502 onto a breadboard. I did a modified 'Ben Eater', where I was driving the clock with a sketch I had written for Arduino Mega 2560. Unfortunately it didn't work, all I got on Address and Data lines was $FF. I don't have a scope, just a cheap TTL/CMOS logic probe. I haven't had time to get back into it, just I do have time while at work to read all these informative posts.

So, in Ben Eater's 6502 build, he doesn't use any pull-ups. When I read the datasheet for the WDC 65C02, I see this on the RDY line.

Quote:

The RDY pin no longer has an active pull up. It is suggested that a pull up resistor be used on this pin when not being used. The RDY pin can still be wire ORed.

I don't see this warning on any other lines, so... to pull-up or to not pull-up (with a resistor).

And what should the value of said resistor be. I see stuff ranges from 330 to 3.3 K.

Help!

Walter

[drogon]

Use a pull-up on Rdy. Also on the BE, Reset, IRQ and NMI inputs, as well as the Abort pin too (65c816 though). I use 3.3KΩ - works for me.

And welcome!

-Gordon

[walter.preuninger]

What are the chances that I fried some silicon?

Thank you

Walter

[GARTHWILSON]

walter.preuninger wrote:

What are the chances that I fried some silicon?

Probably pretty slim; but it's impossible to know without seeing what you did. With CMOS, (or any kind of MOS), you also have to be careful with static-handling precautions while the inputs are accessible to damage with our little mitts. When you reach for the circuit, touch its ground or power before touching any inputs. (You probably already knew that though.)

[walter.preuninger]

Oh, yeah. I am amazed when I see people in YouTube just handling chips like anything else.

I leave my chips in their anti static bag, or transfer them from a tube and rest them on anti static foam. I handle them by the edges.

I don't think my cpu was getting power. I used jumper wire, but my strippers are cheap, and was just using a pocket knife to remove the insulation. I bought some real breadboard jumpers on Amazon, hopefully they will work better. Going to try something tonight.

Thanks!

Walter

[Chromatix]

The W65C02S has "bus holding devices" on most of its pins. They'll hold an input line at a proper CMOS logic level, as long as the CPU is powered - either VCC or GND. But if you want it to settle at a *particular* logic level, then you have to drive it externally - at minimum with a resistor to the appropriate power rail. For historical reasons, most control signals have their quiescent state as logic high, hence the prevalence of pull-up resistors.

[BigDumbDinosaur]

Chromatix wrote:

The W65C02S has "bus holding devices" on most of its pins.

That is not correct. All inputs to the C02 and 65C816 must be driven to Vcc or ground at all times.

[Dr Jefyll]

Doh! You're right, BDD. And, unawares, I just cited this incorrect info in another post.

It's one of WDC's VIAs that has bus hold. On the W65C22S all pins except PHI2 have the bus hold feature. But WDC's W65C22N and their CPU's do not have bus hold.

[BigDumbDinosaur]

Dr Jefyll wrote:

Doh! You're right, BDD. And, unawares, I just cited this incorrect info in another post.

It's one of WDC's VIAs that has bus hold. On the W65C22S all pins except PHI2 have the bus hold feature. But WDC's W65C22N and their CPU's do not have bus hold.

At one time, the 'C02 had a weak pullup on RDY, but that was removed when WDC switched foundries and went to the .6 µm process.