June 26, 2020

Video Timings: VGA, SVGA, 720p, 1080p

To work with standard monitors and TVs, you need to use the correct video timings. This recipe includes the timings for four standard display modes using analogue VGA, DVI, HDMI, or DisplayPort: 640x480 (VGA), 800x600 (SVGA), 1280x720, and 1920x1080 all at 60 Hz.

CRT monitors typically support higher refresh rates in addition to 60 Hz, such as 72 and 85 Hz, but most LCD monitors do not. There are an increasing number of televisions and monitors that do support high refresh rates, but these are beyond the scope of this guide.

This post is part of a series of handy recipes to solve common FPGA development problems. Look out for more FPGA recipes soon.

Feedback to @WillFlux is most welcome.

Video Signals in Brief

Video signals have two phases: drawing pixels and the blanking interval. The sync signals occur within blanking intervals; separated from pixel drawing by the front porch and back porch. Horizontal sync demarcates a line and vertical sync a frame.

Display Timings

Video Timings

Video timings are a complex area with several different specifications, for example, VESA Coordinated Video Timings (CVT) includes four variants for common HD resolutions. This document won’t go into all the variants; instead, we provide conservative timings that should work with all displays. These timings are based on VESA DMT v1.3 (available from vesa.org) and CTA-861-G (available from cta.tech). Other data, such as bandwidths and memory requirements, were calculated by the author.

The frame memory values show how many kilobits (NOT bytes) of memory you need to store a single frame; 12-bit per pixel equates to 4:2:0 Y’CrCb. The data rate is the required bandwidth for 24 bits-per-pixel with the included timings. DVI & HDMI use TMDS encoding: the TMDS clock shown is for regular 24-bit colour, higher colour depths require higher frequency clocks.

VIC is the Video Identification (ID) Code used in EDID. Look out for a post on EDID in future.

VGA 640x480 60 Hz

640x480 is the classic VGA display that works with analogue VGA monitors as well as contemporary HD displays and televisions. I recommend starting with this resolution when developing new display logic; it’s almost foolproof and requires lower clock speeds than HD resolutions.

With analogue LCD monitors, you can usually get away with using a 25 MHz pixel clock. However, based on the VESA tolerance of 0.5%, 25 MHz is not acceptable, and displays could reject it, but I haven’t found this to be a problem in practice. Note that 25.2 MHz is considered acceptable by VESA, which gives a 60 Hz refresh rate (rather than 59.940 Hz).

Exploring FPGA Graphics includes a SystemVerilog design using this display mode.

    Name          640x480p60
    Standard      Historical
    VIC                    1
    Short Name       DMT0659
    Aspect Ratio         4:3

    Pixel Clock       25.175 MHz
    TMDS Clock       251.750 MHz
    Pixel Time          39.7 ns ±0.5%
    Horizontal Freq.  31.469 kHz
    Line Time           31.8 μs
    Vertical Freq.    59.940 Hz
    Frame Time          16.7 ms

    Horizontal Timings
    Active Pixels        640
    Front Porch           16
    Sync Width            96
    Back Porch            48
    Blanking Total       160
    Total Pixels         800
    Sync Polarity        neg

    Vertical Timings
    Active Lines         480
    Front Porch           10
    Sync Width             2
    Back Porch            33
    Blanking Total        45
    Total Lines          525
    Sync Polarity        neg

    Active Pixels    307,200 
    Data Rate           0.60 Gbps

    Frame Memory (Kbits)
     8-bit Memory      2,400
    12-bit Memory      3,600
    24-bit Memory      7,200
    32-bit Memory      9,600

Porch times shown include the border times referenced in VESA DMT.

SVGA 800x600 60 Hz

800x600, or SVGA, offers a little over 50% more pixels than 640x480. The pixel clock for 800x600 at 60 Hz is precisely 40 MHz, which is easy to generate on most FPGAs.

    Name          800x600p60
    Standard        VESA DMT
    VIC                  N/A
    Short Name           N/A
    Aspect Ratio         4:3

    Pixel Clock       40.000 MHz
    TMDS Clock       400.000 MHz
    Pixel Time          25.0 ns ±0.5%
    Horizontal Freq.  37.897 kHz
    Line Time           26.4 μs
    Vertical Freq.    60.317 Hz
    Frame Time          16.6 ms

    Horizontal Timings
    Active Pixels        800
    Front Porch           40
    Sync Width           128 
    Back Porch            88
    Blanking Total       256
    Total Pixels        1056
    Sync Polarity        pos

    Vertical Timings
    Active Lines         600
    Front Porch            1
    Sync Width             4
    Back Porch            23
    Blanking Total        28
    Total Lines          628
    Sync Polarity        pos

    Active Pixels    480,000
    Data Rate           0.90 Gbps

    Frame Memory (Kbits)
     8-bit Memory      3,750
    12-bit Memory      5,625
    24-bit Memory     11,250
    32-bit Memory     15,000

HD 1280x720 60 Hz

The lowest of the common HD resolutions, 720P is widely supported and has relatively modest bandwidth requirements: an 8-bit 720P display requires less than 8 Mbits per frame. Note how the pixel clock of 720P is half that of 1080P (below): this simplifies your design if you need to support both resolutions.

    Name         1280x720p60 
    Standard       CTA-770.3
    VIC                    4
    Short Name          720p
    Aspect Ratio        16:9

    Pixel Clock       74.250 MHz
    TMDS Clock       742.500 MHz
    Pixel Time          13.5 ns ±0.5%
    Horizontal Freq.  45.000 kHz
    Line Time           22.2 μs
    Vertical Freq.    60.000 Hz
    Frame Time          16.7 ms

    Horizontal Timings
    Active Pixels       1280
    Front Porch          110
    Sync Width            40
    Back Porch           220
    Blanking Total       370
    Total Pixels        1650
    Sync Polarity        pos

    Vertical Timings
    Active Lines         720
    Front Porch            5
    Sync Width             5
    Back Porch            20
    Blanking Total        30
    Total Lines          750
    Sync Polarity        pos

    Active Pixels    921,600
    Data Rate           1.78 Gbps

    Frame Memory (Kbits)
     8-bit Memory      7,200
    12-bit Memory     10,800
    24-bit Memory     21,600 
    32-bit Memory     28,800

HD 1920x1080 60 Hz

The 1080P HDMI television or monitor has been the dominant specification for some years. If you’re only going to support one resolution, then 1920x1080 is a solid choice. However, you should bear in mind that the TMDS clock is almost 1.5 GHz, which is demanding for non-transceiver I/O. A full 32-bit 1080P display requires just under 64 Mbits per frame.

    Name        1920x1080p60
    Standard      SMPTE 274M
    VIC                   16
    Short Name         1080p
    Aspect Ratio        16:9

    Pixel Clock        148.5 MHz
    TMDS Clock       1,485.0 MHz
    Pixel Time           6.7 ns ±0.5%
    Horizontal Freq.  67.500 kHz
    Line Time           14.8 μs
    Vertical Freq.    60.000 Hz
    Frame Time          16.7 ms

    Horizontal Timings
    Active Pixels       1920
    Front Porch           88
    Sync Width            44
    Back Porch           148
    Blanking Total       280
    Total Pixels        2200
    Sync Polarity        pos

    Vertical Timings
    Active Lines        1080
    Front Porch            4
    Sync Width             5
    Back Porch            36
    Blanking Total        45
    Total Lines         1125
    Sync Polarity        pos

    Active Pixels  2,073,600
    Data Rate           3.56 Gbps

    Frame Memory (Kbits)
     8-bit Memory     16,200
    12-bit Memory     24,300
    24-bit Memory     48,600
    32-bit Memory     64,800

What about 4K?

The author doesn’t (yet) have 4K-capable displays or FPGA boards, so hasn’t tested timings for 4096×2160 (DCI 4K), or 3840x2160 (4K UHD). Sorry.

©2020 Will Green, Project F