STM32F429 - LTDC Display Size Limit

daemynnur · ‎2016-10-13

Posted on October 13, 2016 at 16:56

The data sheet for the STM32F429 describes the maximum pixel with of the LTDC as 1204 pixels.

However,.. other than CubeMX not allowing the value entered for display width, to be > 1024, I can’t see any reason from the data sheet / reference manual why it can’t be programmed to be greater (e.g. 1280 pixels)

I want to interface a 1280 x120 pixel LCD to an STM32F429

LCD horizontal parameters:

H_Sync = 3

HBP = 54

Active Width = 1280

HFP = 54

As I see it,.

Programming the (horizontal aspects of the) LTDC controller is done via 4 registers.

LTDC_SSCR = HSYNC Width(-1)

LTDC_BPCR = HSYNC Width + HBP(-1)

LTDC_AWCR = HSYNC Width + HBP +Active Width(-1)

LTDC_TWCR = HSYNC Width + HBP + Active Width + HFP(-1)

The active (display) width of the display being the difference between TDC_AWCR & LTDC_BPCR

None of the limits of the programmable values for these register seems to preclude and active width of 1280 pixels.

The horizontal values for the window mapped onto the display are programmed in LTDC_LxWHPCR and appear to be 12 bits wide (i.e. values of 0-4095)

WHSTPOS[11:0]: Window Horizontal Start Position

WHSPPOS[11:0]: Window Horizontal Stop Position

Thus allowing in theory a window up to 4096 pixels wide

Again, nothing there appears to preclude a window width of 1280 pixels.

Unfortunately to try it out will cost me ~ £160 for the display & the time & effort to build a patch for the connection to my hardware, so to save the cost / hassle, only to fail, I’d love someone either tell me if I'm wrong & why, or confirm it is possible.

Thanks in advance

Tesla DeLorean · ‎2016-10-13

Posted on October 13, 2016 at 18:04

Could you at least sanity check with a scope or logic analyzer?

I'm of the belief that some of the spec is to keep bandwidth numbers in check so people don't have expectations of huge displays. I'd expect the counters/comparators to have a specific bit width, be simple in implementation, and not have other odd hard coded limits.

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daemynnur · ‎2016-10-13

Posted on October 13, 2016 at 18:29

''Could you at least sanity check with a scope''

That's a damn good idea, thank you

as for bandwidth, the clock on this display is only ~ 12MHz

(as it only 120 pixels high that still keeps the frame rate up to ~ 70)

so know what the LTDC can do (currently running ~ 25MHz+ on 800x480) I don't see that being a problem