vga 1280 X 1024 need to be at 60 hz

mike goettling

we are using the vga_1280x1024_tile_driver_with_cursor.spin in a progect. we have not changed any settings on it. what we are seeing is it has a refresh rate of 56 hz. the monitors we are using seem to be on the very edge of funtioning. they intermintily start flashing the video and will act as if they are loosing sync. we can reporduce this on a pc if we change it's refresh rate to 56hz.·Is there any way to bump the refresh up to 60 hz? the montors are·name brand.(as if that means much) i can provide more info if needed·

Mike Green

The copy I have of this driver (v0.9 - 22 Nov 2006) says that it produces a 60Hz vertical refresh rate.

Rayman

Just loaded the demo... My monitor says 55.5 Hz.

Rayman

I changed vp to 950 from 1024 and got ~60Hz. But, the cursor isn't happy [noparse]:([/noparse]

Paul Baker

Hi Matt, yes the high resolution graphics can be a bit dodgy on a LCD monitor because the refresh rate is slightly off. CRTs have no issues displaying it, and a sizabale portion of LCD monitors don't either. To make things worse there's no discernable correlation with a statistic suh as cost. There is a slightly stronger correlatiion with manufacturer, it just depends on whether the designer decided to cut corners by providing support for only standard resolutions.

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Paul Baker
Propeller Applications Engineer

Parallax, Inc.

cgracey

All you need to do is replace the 5.00Mhz crystal with at least a 5.40MHz crystal. That will push the overall refresh to 60Hz and beyond.

I suggest using a 6.00MHz crystal, which would·result in a system clock of 96MHz. If the refresh rate is currently 55.5Hz, this 20% speed increase would result in a refresh rate of 66.6Hz, which should be plently. Also, you could knock it back down to something less by lowering the "pr" constant below the current 100 value in the 1280x1024 object.

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Chip Gracey
Parallax, Inc.

hinv

Hi Chip and all,

Do you have a link to a good place to order the right pf 6MHz crystal for the Demo board and the Proto Boards?

Thanks,
Doug

Paul Baker

Any major distributor will stock them (digikey, mouser, jameco, etc). Just make sure it's a HC49 type package (type HC49US is the specific type we use for the products that have removable crystals). You may want to get it from mouser since they don't have a small order surcharge.

If·11.1 fps/MHz is the ratio, this crystal will generate 61 fps, which should be close enough for nearly all monitors to lock. Alternatively you can get a programmable oscillator (some distributors such as digikey will program one to your specified frequency) and program it to 86.486486... MHz for as many decimal places the programmable crystal supports (Programmable oscillators use·a PLL and there can be issues of excessive jitter when a PLL drives another PLL).

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Paul Baker
Propeller Applications Engineer

Parallax, Inc.

Post Edited (Paul Baker (Parallax)) : 3/29/2008 11:09:26 PM GMT

mike goettling

I am running the FullDuplexSerial.spin also on this. will changing the crystal cause an issue with this driver? we are already testing in a store and have not had an issues. this is a nusance issue but we would like to resovle.

Mike Green

As long as you change the _XINFREQ statement in the main object to match your crystal frequency, all of the I/O drivers should be able to adjust themselves. This is true for FullDuplexSerial which uses CLKFREQ to calculate the delay counts from the Baud you provide.

mike goettling

we are ordering a 6mhz and will try that.

Rayman

I just dropped in a 6.25 MHz crystal and the vertical rate increased from 55.5 to 69.2 Hz. All I changed in the code was the _xinfreq command...

hinv

Hi Rayman,

Do you have a link to where you got your crystals? What is the pf and the ppm error?

Thanks,
Doug

Rayman

I have a link here:
http://www.rayslogic.com/propeller/Programming/RaysStuff/RaysStuff.htm

I don't remember·about ppm...

johnfl68

Rayman,

The link for the 6.25MHz Crystal is no longer valid, I guess Alltronics doesn't carry them any more.

Is 6MHz going to be the best choice for this, since it is a bit more common? Mike, did you have any luck with the 6 MHz?

I would like to be able to to 1024x768 and 1280x1024 with the same crystal (switching between each). Just trying to figure out what is going to work the best.

Thanks!

John

mike goettling

we tried the 6mhz crystal but in the end the problem that i am working with is unrlated to the refresh being 55.5hz so we are staying with the 5 mhz crystal. have put the units in one site 12 total per site and is working well.

johnfl68

Is there anything else besides _xinfreq in the spin and adjusting the pr value in the tile drivers that needs to be changed when changing crystals?

I am trying a 6.0 MHz crystal from Citizen, and after adjusting pr (by increments of 5) to get close to 60Hz, and code and images that look fine with the 5.0 MHz crystal, now have jagged pixels along all vertical lines. This is for both crt and lcd monitors.

Has anyone else tried using the tile drivers with a 6.0 MHz or other crystal and seeing this (or not seeing this)?

As mike did, I may just opt to stick with the 5.0 MHz crystal.

Thanks!

John

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