Electronics > Beginners

replace 3.58MHz with 3.579545MHz

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boffin:

--- Quote from: schmitt trigger on December 30, 2019, 03:30:14 pm ---One of my favorite ICs back in the 80s, was a device from National Semi, which generated a 60 Hz signal from a 3.579545 Mhz crystal.

It was a NM-something, and very useful for a timing backup for clocks.

--- End quote ---

We used to use 8870 DTMF tone decoders which also used a colorburst crystal. Always thought it was odd.

Heck, even the original IBM PC ran at a multiple of Colorburst for it's systems clock.  The main crystal was 14.318 (4x colorburst - which was also fairly common) main crystal; which was divided by 4 for the video system (3.579...), and divided by 3 for the main clock @ 4.77MHz


edavid:
(About the MM5369)


--- Quote from: schmitt trigger on December 30, 2019, 04:40:35 pm ---To obtain 60 Hz from an oddball frequency such as 3.579545 MHz, it alternated the frequency’s division ratio.

--- End quote ---
No, it did not, it just divided by 59659.  You had to tweak the crystal load to get it closer to 60Hz.


--- Quote ---As such, the output wasn’t a 50% duty.

--- End quote ---
Yes, that is correct.


--- Quote ---Sadly it is now obsolete, but can be emulated with any modern microcontroller.

--- End quote ---
It was an old PMOS part that wouldn't run at 5V, let alone 3.3V, so it wouldn't be very useful today.

edavid:

--- Quote from: mcovington on December 29, 2019, 09:03:29 pm ---I am not even sure 3.58-MHz (exact, 3.5800000 MHz) crystals have ever been made.  3.579545-MHz crystals are extremely common and are commonly called 3.58-MHz.

--- End quote ---

Here is a datasheet for a 3.580MHz crystal sold by Mouser:

https://www.mouser.com/datasheet/2/741/LFXTAL032257Bulk-997159.pdf

I have no idea why it exists.

james_s:
I've always called the colorburst crystals "3.58 MHz", it's pointless to use gratuitous precision when it's not necessary to do so.

Some applications did make use of this frequency to work with standard definition TV and monitors as displays. In many cases though it was simply the cheapest crystal available since they were made in vast quantities for the TV industry. If you needed something in that general range of frequency it made sense to select 3.58MHz because it was dirt cheap and readily available.

nigelwright7557:
If its just a Z80 clock I cant see why any xtal around that speed wont do.
Unless the same xtal drives a UART or some other time critical device.

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