[Oberon] XGA frequency in FPGA Oberon

[Skulski, Wojciech]

Magnus:

  thank you. This was very helpful. I did not realize that XGA is different from VESA.  The numbers in VID.v look more like XGA than VESA. So it is an XGA display with VESA frequency. The difference is minor, though. The monitors are somehow capable of absorbing the discrepancy, which affects only the horizontal scan. The vertical scan is the same for both VESA and XGA. The number on the left are for VESA.

//Back porch   144   (160 pixels for XGA @ 60 Hz)
//Whole line  1328   (1344 pixels for XGA @ 60 Hz)

Thank you,
Wojtek



________________________________________
From: Oberon [oberon-bounces at lists.inf.ethz.ch] on behalf of Magnus Karlsson [magnus at saanlima.com]
Sent: Tuesday, December 17, 2019 7:53 PM
To: oberon at lists.inf.ethz.ch
Subject: Re: [Oberon] XGA frequency in FPGA Oberon

See tinyvga.com/vga-timing/1024x768 at 70Hz

My guess is that with 25 MHz CPU clock it's a lot easier to generate 75
MHz than 65 MHz.

Magnus

On 12/17/2019 4:31 PM, Skulski, Wojciech wrote:
> All:
>
> we have been playing with the FPGA Oberon firmware and we are puzzled with the peculiar 75 MHz frequency driving the display in Pepino. It actually works with the monitor which we have. People are saying on the web that XGA clock is 65 MHz. See tinyvga.com/vga-timing/1024x768 at 60Hz
>
> NW in his PO.Computer says on page 19 that the frequency should be 56 MHz, rounded up to 60 MHz. So all these numbers are different, 56, 60, 65, and 75 MHz. Does anyone know why? And which one is right?
>
> Thank you,
> Wojtek