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I'm currently designing a TTL-based device to output VGA signals to a 16:9 aspect ratio LCD Monitor with a frame rate of 60 Hz. I hove mostly been referring to this question on how the VGA protocol functions.

I want to be able to calculate how many micro-seconds the H-SYNC and V-SYNC pulses are for 640x360 @ 60 Hz refresh rate. Is their a formula or a table I can refer to to predict the length of the sync pulses?

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  • search on TI's website and read the part's manual and you get all you need to know, or just request a sample – user3528438 Feb 13 '18 at 03:14
  • Since LCD's dont need as much sync time as CRT's the conventional ratios of clock , porches, sync, line should not be the same as 480 which was for CRT's with blanking during retrace. But every monitor has different margins for PLL , so get the monitor specs – Tony Stewart EE75 Feb 13 '18 at 03:54
  • You'll need the required timings from the LCD manufacturer, or else to experiment until you find something that works. Unlike with CRT's, LCD's are generally sampling things and often have a wide lattitude - I once encountered an *LCD vendor demo board* that, either by design or accident, clocked the display at 10 times the rate recommended by their own data sheet! – Chris Stratton Feb 13 '18 at 03:57
  • I once designed a VGA converter for Kopin's AMLCD and a CRT based Ultrasonic displays, but that was over 15 yrs ago. Are thinking of this display or something else? https://www.aliexpress.com/store/product/for-INNOLUX-7-0-inch-Raspberry-Pi-LCD-Display-Screen-TFT-LCD-Monitor-AT070TN90-Kit-HDMI/809667_32621426867.html – Tony Stewart EE75 Feb 13 '18 at 04:05

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It depends on the sink (monitor) but most computer displays and display controllers accept VESA standard timings, either from the VESA Display Monitor Timing (DMT) or VESA Generalized Timing Formula (GTF). VESA is the Video Electronics Standards Association, a standards body for computer display standards. In contrast, most displays for televisions/broadcast/movies accept CEA timings, specified in EIA-CEA-861. The relevant VESA documents were open to the public until recently and are still readily available; CEA-861 is available for a fee but there are older revisions somewhere out on the interwebs.

VESA DMT and CEA-861 are both tables of resolutions, giving the standard timing for common resolutions. However, IIRC, 640x360 is not in either, and therefore VESA GTF is your best bet (unless your sink has an EDID that tells you otherwise). My copy of the VESA GTF (it's just a spreadsheet, easily found with Google) tells me 640x360@60 corresponds to an Hblank of 7.447 us and Vblank of 0.581 ms, among other things. I would highly recommend glancing over the VESA DMT and playing around with the VESA GTF spreadsheet, it's quite educational.

Note: the VESA free standards used to be open to the public. Sadly, it seems that is not the case any longer and you now have to be a VESA member. Also, there is a Linux utility aptly named gtf which will happily calculate GTF timings for you.

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