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Topic: Help with doubling frequency. (Read 1 time) previous topic - next topic

dc42

Rather than using a couple of inverters to delay the signal, if might be better to get a longer and more controlled delay by using a delay line, for example http://para.maximintegrated.com/en/search.mvp?fam=del_line&295=Tapped&hs=1. Alternatively, use 2 of the inverters in a 74HC14 with an R-C network connected between them.
Formal verification of safety-critical software, software development, and electronic design and prototyping. See http://www.eschertech.com. Please do not ask for unpaid help via PM, use the forum.

pYro_65

Yeah, i'm not sure if it is accurate either,  

The UTFT and others aren't taking advantage of the displays hardware capabilities ( not in data sheet either ), they set data into the the parallel outputs ( colour info ) then pulse WR once. This 'set colour & strobe' is repeated for the fill. In mine, WR is simply pulsed.

I'm already pulsing the LCD as fast as the mega can write. Which is why even, without a frequency doubler I want to use a low-order port to provide the pulse as the high-order ports ( lcd shield connection ) require atomic blocking, effectively halving the toggle speed.

I'll start to de-solder the shield pin now, to see if a simple pin change has any effect, then I'll at least give frequency doubling a go.
I'm curious to see it run even close to 130 fps.

I'll post on how it goes.

Just saw your post dc42, will check it out.

pYro_65

Seems the WR line is already on a low order port. And wouldn't 130 fps require the MCU to run at 20 mhz so it can clock out pixels at 10Mhz on single instruction pin changes?

Krupski


Hi, I have an LCD that I want to speed up using an external circuit.


First of all, an LCD has it's own internal processing time. No matter how fast you pulse the enable pin, the LCD can only work as fast as it's able.

Secondly, the physical response time of an LCD screen is slow (in the millisecond range). What benefit do you get from accessing it faster?

Lastly, if you know your clock speed, you can make a delay circuit of about 1/2 the period of the clock then XOR the two together and get a 2X clock.

It all seems pointless though (unless I'm missing something).
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dc42

Are you using the SPI pins for anything? If you use the SCLK pin as your WR line, you can get a hardware clock from it at half the crystal frequency by doing a dummy SPI transfer.
Formal verification of safety-critical software, software development, and electronic design and prototyping. See http://www.eschertech.com. Please do not ask for unpaid help via PM, use the forum.

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