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Author Topic: BT81x to support 1366*768 LCD?  (Read 209 times)

techtoys

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BT81x to support 1366*768 LCD?
« on: January 16, 2019, 09:26:21 AM »

It is stated on datasheet of BT81x that the max PLL frequency reaches 72MHz. Regarding this I wish to ask if BT81x can support a LCD of 1366*768 with pixel clock typ. @ 70MHz?

Attached jpg is a screen shot from the LCD's datasheet on timing data.

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Re: BT81x to support 1366*768 LCD?
« Reply #1 on: January 17, 2019, 10:42:45 AM »

Hello

Using BT81x @ 72MHz system clock, it is possible to achieve 30Hz refresh rate for a 1366x768 display, less than the standard 60Hz.
 
In case the display supports Adaptive Frame Rate(AFR) operation, then it’s possible to get 60Hz refresh rate by set REG_PCLK=1. If AFR is not supported (for LVDS display), the display list shall be less complicated, similar to the performance achieved by our 10” HD demo at Electronica 2018 (1280x800 60Hz).
 
The EVE series of ICs do not include a frame buffer, they dynamically clock out each computed pixel on the screen. A displays size and what the Pixel Clock is running at will determine the achievable performance. It is also worth noting using larger displays reduces the computational time available for each pixel on the screen.

If we take the example from the following WQVGA settings:
Code: [Select]
    // WQVGA display parameters
   lcdWidth   = 800;                                                            // Active width of LCD display
   lcdHeight  = 480;                                                            // Active height of LCD display
   lcdHcycle  = 928;                                                            // Total number of clocks per line
   lcdHoffset = 88;                                                             // Start of active line
   lcdHsync0  = 0;                                                               // Start of horizontal sync pulse
   lcdHsync1  = 48;                                                            // End of horizontal sync pulse
   lcdVcycle  = 525;                                                           // Total number of lines per screen
   lcdVoffset = 32;                                                            // Start of active screen
   lcdVsync0  = 0;                                                              // Start of vertical sync pulse
   lcdVsync1  = 3;                                                              // End of vertical sync pulse
   lcdPclk    = 2;                                                                  // Pixel Clock
   lcdSwizzle = 0;                                                              // Define RGB output pins
   lcdPclkpol = 1;                                                              // Define active edge of PCLK
 
             

HCYCLE = 928
VCYCLE = 525
VCYCLE * HCYCLE  = 487,200

Note: REG_PCLK is using the value 2 which will divide the clock down to 30Mhz.

Result = 30,000,000/487,200 = ~ 61 fps

Best Regards,
FTDI Community
« Last Edit: January 17, 2019, 10:45:27 AM by FTDI Community »
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techtoys

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Re: BT81x to support 1366*768 LCD?
« Reply #2 on: January 18, 2019, 12:13:38 PM »

Hi

Thank you for the quick response. You have mentioned "The EVE series of ICs do not include a frame buffer, they dynamically clock out each computed pixel on the screen." In this case, the concept of framebuffer to store/swap a frame cannot apply. Therefore 1366*768*2bytes for a full frame can be ignored, right?

If the GRAM is not a frame buffer, suppose I have some bitmap data as an array pointed by uint16_t *fb, where this bitmap data should be copied to Eve in order to get it displayed?

Asking this question because 1366*768*2 = 2MBytes > 1MBytes CGRAM in Eve. At the beginning I was worried by this equation.

A frame frame of 30Hz may be enough good but a test is required. Is there any Youtube video or something to show your 10” HD demo at Electronica 2018 (1280x800 60Hz)?

Best Regards

John
« Last Edit: January 19, 2019, 01:55:35 PM by techtoys »
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Re: BT81x to support 1366*768 LCD?
« Reply #3 on: January 21, 2019, 01:36:46 PM »

Hello John,

Yes, That is correct.

The following Application note covers the basics of working with bitmaps in EVE, including loading them into GRAM:
https://brtchip.com/wp-content/uploads/Support/Documentation/Application_Notes/ICs/EVE/AN_314_FT800_Advanced-Techniques_Working-with-Bitmaps.pdf

Unfortunately there currently isn't a video of the demo on YouTube, but we plan on uploading one in the near future. I may be able to take a short video of the demo running on my desk and upload this within the next couple of days if that would be helpful to you?

Best Regards,
FTDI Community
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techtoys

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Re: BT81x to support 1366*768 LCD?
« Reply #4 on: January 21, 2019, 04:29:01 PM »

Hi

A video from your desk will definitely be useful. Look forward to it. It is not hurry.

After studying AN_314 there are still some follow-up questions. On page 4 it states that "The internal graphics RAM of the FT800 is 256k Bytes and as such any image stored on chip must fit into this memory size."
For new BT81x the graphics RAM is 1M bytes. This translates to something like 1366*732*1 byte. Does it mean we cannot fit in a full frame of 1366*768 of 565 color in BT81x? If this is true, how a larger screen of 1280*800 from your desk is supported?


John
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Re: BT81x to support 1366*768 LCD?
« Reply #5 on: January 22, 2019, 12:00:10 PM »

Hello John,

Yes that would be correct a quick run of the maths for a RGB565 image on a 1366*732 screen works out to roughly 2M Bytes. Such a bitmap would be too large for the internal graphics RAM on the BT81x. The BT81X ICs include support for external flash memory which can be used to store/offload graphics elements such as bitmaps, custom fonts and widgets from the integrated RAM, using ASTC:
You can find out more info at the following page (see programmers guide):
http://brtchip.com/bt81x/

Is there a specific reason you are trying to use a full screen bitmap?

Best Regards,
FTDI Community
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techtoys

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Re: BT81x to support 1366*768 LCD?
« Reply #6 on: January 22, 2019, 03:15:43 PM »

The reason is that, there is a potential application to show a life video from cmos sensor. We wish to use a large display of 1366*768 to display it in full frame but don't know if it is possible. If not, we would be forced to use a LCD panel of lower resolution.
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