128MHz frequency on port pin

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#1
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As we know, CLKper4 can be appeared on some port pins (except A series) and the maximum allowable frequency for this clock is 128MHz. Also according to datasheets, the typical pin rise time is 4ns. I asked Atmel support for maximum frequency of port pins (PC7,PD7,...) when CLKper4 will be output to port pin, but the answer does not contain any new information:

Quote:
For XMEGA AU devices, you can choose which of the peripheral clocks
(CLKper, CLKper2 or CLKper4) will be output to the port pin with the
CLKOUTSEL bits in the CLKEVOUT register.

The clock output option on XMEGA A devices can only output the CLKper.

Ozhan KD
Knowledge is POWER

Last Edited: Mon. Jan 27, 2014 - 06:45 AM
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I am still waiting for Atmel response since december 16.

Ozhan KD
Knowledge is POWER

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The max I have managed is 64MHz out on a pin.
But this is using the internal 32MHz osc running through the PLL up to 64MHz.

The output was very clean, and drove a 10ns external SRAM (low address bit) just fine.

If you manage 128Mhz, I would indeed be interested!

Brad

I Like to Build Stuff : http://www.AtomicZombie.com

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Thanks Brad. If XMEGA can generate 128MHz on port pin, my opinion is to use it as a RF signal generator by changing prescalers and PLL factor. Also It is interesting to try building an FM transmitter by changing oscillator calibration bytes.

Ozhan KD
Knowledge is POWER

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After 10 days, this is the Atmel reply:

Quote:
As mentioned in the manual, For XMEGA AU devices, you can choose which of the peripheral clocks (CLKper, CLKper2 or CLKper4) will be output to the port pin with the CLKOUTSEL bits in the CLKEVOUT register.
The clock output option on XMEGA A devices can only output the CLKper.
To create a clock on Xmega output pin, one option is use PLL as `clk-sys' source and enable clockout option either from pin PC7 or PD7 or PE7 .By considering the required clock output value, select input clock source value, proper multiplication factor in PLL and prescaler values in System clock Prescaler.

:shock:

I wrote again:

Quote:
I know how to setup registers for generating CLKper4 on port pins. But my question is :

Is it possible to generate "128MHz" on PC7,PD7 or PE7?
My question is about the MAXIMUM POSSIBLE FREQUENCY ON PORT PIN. Is it 128MHz? In other words, if CLKper4 is 128MHz, can PC7,PD7 or PE7 generate this high frequency?

Ozhan KD
Knowledge is POWER

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Shirley, you can just try it for yourself.

The PLL will 'function' way beyond the official data sheet limits. I am sure that Atmel will never recommend anything outside of the spec.

But if it works for you, go for it.

I can't see any overheating or damage can arise. OTOH, it would be unwise to design a commercial product on this basis. Especially since there are plenty of PLLs and VCO chips out there. (which are in spec)

David.

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128MHz is not an out of range value for CLKper4.
Maximum recommended values:
CLKper4=128MHz
CLKper2=64MHz
CLKper=32MHz
and all of these clocks can be appeared on special pins.

Ozhan KD
Knowledge is POWER

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Good news from Atmel:

Quote:
I've mounted ATXmega64A3U device in STK600 and I've taken out 128MHz clock from PD7 pin. Please find the attached snapshot and the code used.

Attachment(s): 

Ozhan KD
Knowledge is POWER

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Very cool!
Your code was not attached though.

I will try it on my XMega384 and verify for you.

Brad

I Like to Build Stuff : http://www.AtomicZombie.com

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electronic.designer wrote:
Also It is interesting to try building an FM transmitter by changing oscillator calibration bytes.

I did it, it works. By connecting the amplified signal of an electret microphone to ADC input and changing RC32M calibration value by ADC results and using a simple wire as antenna, I heard my voice on FM radio.

Ozhan KD
Knowledge is POWER

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But that you can do with lower freq. as long you make a modulated signal on a 1/3 1/5 1/7 1/9 etc all the odd harmonics.
Just try to run a normal AVR at 15MHz the noise at 105MHz on the radio will be gone!

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Quote:
Please find the attached snapshot

Am I misreading that, or is it something like 120mV p-p ?

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Vp-p is approximately 1.2v (200mv/div for C3).

Ozhan KD
Knowledge is POWER