Small TFT based on ILI9341 ST7789 - how to use - Page 5

Small TFT based on ILI9341 ST7789 - how to use

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aBUGSworstnightmare: Posts: 13432; Joined: Tue Jun 30, 2015 1:35 pm

Re: Small TFT based on ILI9341 ST7789 - how to use

Quote

Thu Oct 30, 2025 8:59 am

3.2.4. Graphic RAM (GRAM)
The GRAM is used to store the display pattern data with a maximum of 345,600 bytes for 320 (RGB) x 480 display
resolution.

come on dude ... where is your math? what does offset x or y result in?

One can try that on a 480x320pixels display for sure -> adding

Code: Select all

y-offset=20

to config.txt will result in a downward shift of the start position by 20 pixels, causing an overflow that will be shown on top

y-offset.jpg: y-offset=20 added -> shifted downwards; y-offset.jpg (229.87 KiB) Viewed 437 times

so, lets add

Code: Select all

x-offset=20

instead. What is the expected result? Right, an overflow to the right which will result in a skewed image because the 20pixels will be shifted from the end of line1 into the start of line2.

x-offset.jpg: x-offset=20 added -> skewed image as remaining pixels from each scan line will be shifted into the next scan line. Check the RAM addressing in the datasheet; x-offset.jpg (221.67 KiB) Viewed 437 times

Still having the changed start position (x-offset) in my config.txt I will leave it to you to figure out how to achieve a stable image anyway :idea:

x-offsetbutstable_whatsthetrick.jpg: x-offset=20 added to config.txt but stable anyway!; x-offsetbutstable_whatsthetrick.jpg (218 KiB) Viewed 437 times

robertojguerra: Posts: 114; Joined: Thu Dec 05, 2024 6:35 pm

Re: Small TFT based on ILI9341 ST7789 - how to use

Quote

Thu Oct 30, 2025 4:57 pm

Is the solution something related to the graphic ram access cmmands? (I just saw that the command opcodes are the same between st7796, ili9486 and ili9488)

command 0x2A 0x__ 0x__ 0x__ 0x__ #column address set
command 0x2B 0x__ 0x__ 0x__ 0x__ #page address set

Do you have your lines and columns in reverse order for 180 degree rotation?

command 0x36 0x20 #memory access control. 0x20 pins right. 0xE0 pins left

Is the solution involving the timing parameters in the DTS?
hback-porch = <0>;
vback-porch = <0>;
hfront-porch = <0>;
hsync-len = <0>;
vfront-porch = <0>;

aBUGSworstnightmare: Posts: 13432; Joined: Tue Jun 30, 2015 1:35 pm

Re: Small TFT based on ILI9341 ST7789 - how to use

Quote

Thu Oct 30, 2025 5:30 pm

robertojguerra wrote: ↑
Thu Oct 30, 2025 4:57 pm
Is the solution something related to the graphic ram access cmmands? (I just saw that the command opcodes are the same between st7796, ili9486 and ili9488)

command 0x2A 0x__ 0x__ 0x__ 0x__ #column address set
command 0x2B 0x__ 0x__ 0x__ 0x__ #page address set

Do you have your lines and columns in reverse order for 180 degree rotation?

command 0x36 0x20 #memory access control. 0x20 pins right. 0xE0 pins left

Is the solution involving the timing parameters in the DTS?
hback-porch = <0>;
vback-porch = <0>;
hfront-porch = <0>;
hsync-len = <0>;
vfront-porch = <0>;

somehow, nope, nope and nope!

you are 2pixels off (x-offset=2) (with a CCC display) then i.e width=240 gets changed to width=238

robertojguerra: Posts: 114; Joined: Thu Dec 05, 2024 6:35 pm

Re: Small TFT based on ILI9341 ST7789 - how to use

Quote

Fri Oct 31, 2025 6:25 am

Ok, I figured it out... to have a 2 pixel offset to the right, we need in the config.txt:

dtoverlay=mipi-dbi-spi-format-parameter,spi0-0,speed=60000000
dtparam=compatible=4in0円panel-mipi-dbi-spi
dtparam=width=478,height=320,width-mm=35,height-mm=28
dtparam=reset-gpio=25,dc-gpio=24
dtparam=write-only,cpha,cpol
dtparam=format=b6x2g6x2r6x2
dtparam=x-offset=2
dtoverlay=ads7846,cs=1,penirq=23,speed=1000000,keep_vref_on=1,swapxy=1,xohms=60

Now all the console characters show 100%, and the cursor doesn't get shaved off in the GUI :D

aBUGSworstnightmare: Posts: 13432; Joined: Tue Jun 30, 2015 1:35 pm

Re: Small TFT based on ILI9341 ST7789 - how to use

Quote

Fri Oct 31, 2025 8:58 am

robertojguerra wrote: ↑
Fri Oct 31, 2025 6:25 am
Ok, I figured it out... to have a 2 pixel offset to the right, we need in the config.txt:

dtoverlay=mipi-dbi-spi-format-parameter,spi0-0,speed=60000000
dtparam=compatible=4in0円panel-mipi-dbi-spi
dtparam=width=478,height=320,width-mm=35,height-mm=28
dtparam=reset-gpio=25,dc-gpio=24
dtparam=write-only,cpha,cpol
dtparam=format=b6x2g6x2r6x2
dtparam=x-offset=2
dtoverlay=ads7846,cs=1,penirq=23,speed=1000000,keep_vref_on=1,swapxy=1,xohms=60

Now all the console characters show 100%, and the cursor doesn't get shaved off in the GUI :D

you nailed it!

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