Hi,

I have question about making clock circuit on 6502 mpu with on-chip clock oscillator (1 MHz). Those old scanned manuals I found on the web says that it requires single phase time-base input and it can be either a crystal or rc circuit. What I'd like to know is what frequency should I use for time-base? Should it be higher than 1 MHz (2, 3 MHz) or not?

I found 1.0000 MHz crystal relatively too expensive (500% of the 4MHz one!) Some will say I should use in-one-piece TTL oscillator rather than wiring osc. circuit. Well I would, if I could get one! Here no one even heard of 1.000 MHz osc. (the slowest one I could find was ~2.6 ...)

Thanks for all replies.

Hi,
Welcome to the group.

For an original NMOS 6502, the phase-0 input frequency is 1 Mhz (or less - I don't remember what the minimum speed is).

However, there are many 6502A's, which are rated for 2 Mhz. This chip was used in lots of early machines, such as the Commodore VIC-20. Look closely on the chip for the "A" - it was often stamped on the device separate from the normal markings, because they were "select in test" devices: in manufacturing, they tested the part at different speeds, and if it worked at 2 Mhz, it got the "A" stamp. Otherwise, they sold it as a 1 Mhz part.

I also have a 6502B, which is supposed to run at 3 Mhz.

Also, there is a 6502C that was used in the Atari 800 computer, but it is *not* a 4 Mhz part; rather it is 2 Mhz. The "C" is because it has some minor difference in the bus signals. As far as I know, only Atari used this version.

The original brands are MOS Technology (*not* the same as Mostek), Rockwell, and Synertek. The earliest dates are 1976 I think.
[ This reminds me: if anyone in the group has an early chip that they would trade for something else, let me know. First choice would be a 6502 that does not implement the ROR instruction. It would probably have an early 76 date code. ]

In "modern times", there are now CMOS 65C02 parts, which are available at up to 14 Mhz. I think they are all marked such as "W65C02-10", which is a 10 Mhz part.
Western Design Center is the primary vendor of the C02, but there are 2 or 3 other brands also, I think.

Pete

Hi Pete,

First, the minimum frequency specified is 50 kHz. As I understand now clock frequency of mpu depends on input frequency (Ph0). What is difference with mpu's without on-chip clock oscillator anyway? Is that they need two phase clock input rather than single and nothing else?

Yagwa

Yes, I think so: the 6501 required an external 2-phase non-overlapping clock. It was made to be very compatible with the 6800, but I think was only made for a very short time. [ Has anyone ever seen one?? ].

With the 6502, you give it a single-phase clock on the "phase-0" pin, and it generates phase-1 and phase-2 internally.
Phase-0 and phase-2 are in the same phase, while phase-1 is 180 degrees out. Of course, phase-2 ends up being slightly later than phase-0.

Pete

I've still got some of the old Synertek NMOS 6502-C parts, clearly spec'd at 4 MHz. These have the same instruction set as the MOS-Technology parts. I routinely used them with that instruction set and software.

Rockwell made CMOS versions with instruction set extensions, some with the normal clock arrangement and a 'C102 version with the extended instruction set but a 4x clock, which worked like the 6809's clock. Those were commonly available in 1 through 4 MHz speed grades and were selected for faster parts.

The way to clock your 6502 is to use a fast crystal oscillator and use a counter to prescale the clock to the rate you desire, which you then feed to the Phase-0 input of your CPU. A 1K pullup resistor may help the clock a little bit, but isn't really necessary. When you time your read and write strobes, be sure you gate your write signal with phase-0 rather than phase-2, else you'll have data-hold-time vilations with almost any memory or LSI you use. In general, it's safe to use the CPU's read/write-not or'd with phase-0-not. You can save some wiring effor if you use an 'LS145 or similar part, to which you feed the phase-0, phase-2, and read/write-not at the address inputs, and use the remaining signal as an enable. What's convenient about the '145 is that it's an open collector driver, allowing you to tie outputs together. A PAL could do this as well and more efficiently.

This is worth considering as you speed up your CPU.

good luck!

Uli

I've still got some of the old Synertek NMOS 6502-C parts, clearly spec'd at 4 MHz. These have the same instruction set as the MOS-Technology parts. I routinely used them with that instruction set and software.

Rockwell made CMOS versions with instruction set extensions, some with the normal clock arrangement and a 'C102 version with the extended instruction set but a 4x clock, which worked like the 6809's clock. Those were commonly available in 1 through 4 MHz speed grades and were selected for faster parts.

The way to clock your 6502 is to use a fast crystal oscillator and use a counter to prescale the clock to the rate you desire, which you then feed to the Phase-0 input of your CPU. A 1K pullup resistor may help the clock a little bit, but isn't really necessary. When you time your read and write strobes, be sure you gate your write signal with phase-0 rather than phase-2, else you'll have data-hold-time vilations with almost any memory or LSI you use. In general, it's safe to use the CPU's read/write-not or'd with phase-0-not. You can save some wiring effor if you use an 'LS145 or similar part, to which you feed the phase-0, phase-2, and read/write-not at the address inputs, and use the remaining signal as an enable. What's convenient about the '145 is that it's an open collector driver, allowing you to tie outputs together. A PAL could do this as well and more efficiently.

This is worth considering as you speed up your CPU.

good luck!

Uli

>I've still got some of the old Synertek NMOS 6502-C parts, >clearly spec'd at 4 MHz. These have the same instruction set >as the MOS-Technology parts.

Yes, I've seen the 6502C in a Synertek data book just recently (never seen the actual chip yet - wanna trade one for something?).

But I think the one in the Atari 800 is made by someone else; and I recall a web page that described what was different about it - I think it was in the use of the control lines, not in the instruction set (?).

Pete

For now I'm haning onto these old parts. Why not order you a part from WDC? Surely they have dealers. I've had no need to get with them so far, though I may.

I don't know what the differences are, but what you might do is contact the guy who runs the 6502.org web site and see what he can tell you. He's supposedly building some hardware, so he must know something about these various parts. He once claimed that WDC was offering a 20 MHz 6502, but that just showed he doesn't understand the difference between a 6502 and the part (a 65HC816) which they did offer at 20 MHz. Nevertheless, he should know where you can get something suitable for your needs.

If you have further questions, feel free to email me as <edick_at_idcomm_dot_com>.

regards,

Uli

>For now I'm haning onto these old parts. Why not order you a >part from WDC? Surely they have dealers. I've had no need to >get with them so far, though I may.

I don't want one for the speed, it's for the 'history'.
For the same reason, I'm watching for a real early 6502 that doesn't have the ROR implemented.

>...the guy who runs the 6502.org web site and see what he >can tell you. ...but that just showed he doesn't understand >the difference between a 6502 and the part....

Did you know that you're talking about the 'host' of this forum?

Pete

Yes, I do know that the guy to whom I refer in my comment about the distinction between those two processors hosts this discussion.

However, we all have opinions and we all have information, sometimes differing from what others have. Because of this, it's important we don't allow comments we make to blur the line between the two.

Before "rolling my own" 650x core, I wanted to make certain I couldn't buy a conveniently packaged part from WDC or someone else. While I could buy someone else's IP to implement in an array, I've yet to find one that's fast enough and thrifty enough to satisfy me.

His comment that there was a readily available 20MHz 65SC02 sent me off on a week-long search culminating in a pointless effort to determine whether and when I could obtain and physically test/examine a few of these babies. When I checked with him about this apparent misstatement of fact, I got no response from him. Now, we all sometimes overload our position in the course of discussion, but this was a bit confusing to me, since I'd have assumed the underlying knowledge about the WDC 65SC... line was there.

Though I have extensive contacts throughout the industry, I've encountered no one who's seen a WDC 6502. It's quite possible that they simply don't have such a part ready for sale.

Uli

> I've encountered no one who's seen a WDC 6502. It's quite >possible that they simply don't have such a part ready for >sale.

Do you mean *any* WDC 6502, or a 20 Mhz one?
There are plenty WDC 65C02's around - I've got some...

Pete

That's reassuring. Do you have any of the 14MHz parts? I'm convinced that there's no packaged 20 MHz part, though they may well run that fast. They claim to have a 20 MHz core, but that's IP, not silicon.

How about the package, do you have any in a DIP40? DO they drop in as a replacement for the earlier 6502 CPU's. SOme of the signals on the PLCC don't look right. I've got to pore over the data sheet a bit. It looks as though I may have to roll-my-own in order to get the right instructions and enough speed.

Would you happen to have a complete list of the 6502 opcodes including the undocumented ones? I've completely lost track of mine.

Uli

regards,

I believe that both the CMOS versions of the 6502 from CMD and WDC are pin-compatible in the DIP40 package. I know Pete has dropped a WDC 65C02 in his VIC-20 with no problems.

Check out the Programming & Source Code page on www.6502.org for the opcodes, including the undocumented ones.

_________________
- Mike Naberezny (mike@naberezny.com) http://6502.org

I revisited the data sheet on the WDesignC web site and found that while there's an entry for the DIP40 package, there's nothing in it, suggesting that the PLCC44 is the only currently available package. It looks to me as though there are a few extra signals available there. Has anyone ever dealt with this?

Uli

>That's reassuring. Do you have any of the 14MHz parts?

No. Jameco has -10's, in 40-DIPs.

>How about the package, do you have any in a DIP40? DO they >drop in as a replacement for the earlier 6502 CPU's.

As Mike said, I plugged in a 65C02 in a VIC-20, and it worked fine (I did it to save power for a battery-powered robotics project). Then I replaced the two 6522's with 65C22's, and it also worked fine, and saved even more power (the 65C22's are not WDC, they are another obscure brand, but I found them on the web).

Go to 6502.org, follow the link to "Pete's Robot", and you'll find pictures, schematics, etc.

Pete