differential clock output

Technical questions regarding the xTIMEcomposer, xSOFTip Explorer and Programming with XMOS.
MastaTabs
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Posts: 4
Joined: Thu Jan 14, 2010 3:18 am

differential clock output

Postby MastaTabs » Mon Feb 01, 2010 12:51 am

Hi,

I'm trying to interface an L1-64 to a chrontel DVO chip to possibly get an dvi/tv out going.
To do that I need two sychronus clock signals, one of them is the invert of the other.

I've been trying it this way:

Code: Select all

out port XCLK = XS1_PORT_1M;
out port XCLKI = XS1_PORT_1N;

int main() {
	configure_clock_rate( clk , 100 , 2); // 27/1 = 27 Mhz
	configure_port_clock_output( XCLK , clk );
	set_port_inv(XCLKI);
	configure_port_clock_output( XCLKI , clk );
	start_clock(clk);
	return 0;
}
I only get an output on the first not inverted clockoutput, not on the inverted one.

Any ideas or insights ?

Thanks
Tobias
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paul
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Joined: Fri Jan 08, 2010 12:13 am

Postby paul » Mon Feb 01, 2010 2:25 am

Hmmm... I am not entirely sure what you are attempting in that code is legal/possible. Have you run this on the simulator and got a waveform trace? I had a quick look at the chrontel stuff and the CH7301, 7010 and 7302 datasheets say something in the form of:
External Clock Inputs
These inputs form a differential clock signal input to the CH7301C
for use with the H, V, DE and D[11:0] data. If differential clocks
are not available, the XCLK* input should be connected to VREF.

The output clocks from this pad cell are able to have their polarities
reversed under the control of the MCP bit (in register 1Ch).
So this might be a pointless exercise as it looks like you can use a normal clock...?
Paul

On two occasions I have been asked, 'Pray, Mr. Babbage, if you put into the machine wrong figures, will the right answers come out?' I am not able rightly to apprehend the kind of confusion of ideas that could provoke such a question.
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paul
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Joined: Fri Jan 08, 2010 12:13 am

Postby paul » Mon Feb 01, 2010 2:35 am

Also, out of interest what kind of resolution are you hoping for? DVI usually requires extremely high data rates as it is generally aiming at high bits per pixel and high pixel count signal...
Paul

On two occasions I have been asked, 'Pray, Mr. Babbage, if you put into the machine wrong figures, will the right answers come out?' I am not able rightly to apprehend the kind of confusion of ideas that could provoke such a question.
MastaTabs
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Posts: 4
Joined: Thu Jan 14, 2010 3:18 am

Postby MastaTabs » Mon Feb 01, 2010 12:43 pm

Thanks man. I somehow overlooked this in the datasheet.

At first I'd be happy with something 640x480 or possibly 800x600.
The idea was to use the XMOS as somekind of conversion pipeline for retro computer graphics output. Grab it digitaly and pipe it modified to dvi or svideo or ...

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