SY6502 at 3.579545Mhz???

cbmeeks · Post by **cbmeeks** » Wed Aug 17, 2005 12:11 am

I have a SY6502 and I am going to use it to build a home-computer.

I would like to clock it at 3.579545 Mhz (the NTSC sub-carrier). I have a few 3.579545 crystals but didn't want to try it because I don't know what would happen (I only have one 6502).

I can't seem to find the datasheet either.

Any thoughts?

Thanks!

cbmeeks

GARTHWILSON · Post by **GARTHWILSON** » Wed Aug 17, 2005 6:19 am

There's definitely no need to treat your µP like it's the only one left. They are being made today and those are rated for a minimum of 14MHz and are much better from a standpoint of instructions and addressing modes, bugs, power consumption, control pins, voltage operation range, bus-driving capability, onboard clock generation, and ability to stop the clock than what you have. You can buy them directly from Mike Naberezny here on this website or even from the manufacturer, WDC. The data sheets can also be found on this website.

If you must use an old NMOS 6502, be aware that without any sufixes on your part number, it's a 1MHz part, which means it might have passed the tests at 2MHz but not 4MHz (or close to it). Since you're just getting started and you're not trying to support legacy code or hardware, I would recommend bypassing the NOMS 6502 and going directly to the CMOS 65c02.

cbmeeks · Post by **cbmeeks** » Wed Aug 17, 2005 12:20 pm

Thanks for the tip.

I should probably say that I am going for as much "retro-ness" as possible with my homebrew computer. Basically, a 6502 driving everything and SX28/52 for the audio/video subsytems.

I may just put a 1Mhz crystal in there until I can afford some variants of the 6502 (newer models).

Thanks!

cbmeeks

GARTHWILSON · Post by **GARTHWILSON** » Wed Aug 17, 2005 6:19 pm

> I may just put a 1Mhz crystal in there until I can afford some variants
> of the 6502 (newer models).

You can't just put a crystal on an NMOS 6502 like you can on a CMOS one. The NMOS ones required an external clock oscillator. If exact clock speed is not critical, the CMOS ones even allow you to just hang a resistor and capacitor between pins 3, 37, and 39. 5.6K and 68pF give you about 1MHz.

As far as cost-- There have been some suppliers that have gotten some old, slow NMOS 6502's and wanted to sell them for up to $20 each thinking they really had a treasure, but the new ones are only about a quarter of that price.

cbmeeks · Post by **cbmeeks** » Fri Aug 19, 2005 2:02 pm

oh, OK...thanks for the tip!

cbmeeks

Raf · Post by **Raf** » Fri Aug 19, 2005 3:01 pm

well.. I havbe read a text about 6502 history and one of engineers said he was running 6502s meant to be used as 1MHz at (incerdilby at around 1975) 10MHz - maybe someone can comment this?