EPD 7.5 v2: Partial window has issues and displays garbage most of the time

[NorbertRoller]

Connected to the ESP32 DEV Modul.

I tried the Examples of "esp32-waveshare-epd" "epd7in5_V2-demo"

Issue 1:
With the example Font20 and 7 characters the partial display works!
Any iteration Font16 or 8 characters displays garbage unless the x-start is set to 0. The Y-Position doesn't matter.
By checking what is transferred to the EPD, I have confirmation that the start and end position is calculated correct. Regardless of different fonts or x-start or number of characters.
The Function (EPD_7IN5_V2_Display_Part) is defined in EPD_7in5_V2.cpp (located it Arduino\libraries\esp32-waveshare-epd\src\utility) and this file is a version 3 of 2023-12-18
Until I completely wrong, this must be an issue of the GPU driving the EPD and therefore it can not been fixed in the sample code / Library unless the code on the EPD itself can be flashed.
Can someone verify if this assumption is correct or when not help to fix the code, please

Issue 2:
I have spend several hours to find the issue and have obviously compared the code against the documention.
I believe that the documentation (https://files.waveshare.com/upload/6/60/7.5inch_e-Paper_V2_Specification.pdf) page 25 doesn't match the screen.
The function: EPD_7IN5_V2_Display_Part (.....) sets the partial mode and uses the full 8 bits to address x-start and x-end while the documentation only wants HRST[7:3] to be used. Obviously this would only address 64h horizontal dots. Not enough for this display.
The code addresses 7:0.

EPD_SendCommand(0x91); //This command makes the display enter partial mode
EPD_SendCommand(0x90); //resolution setting
EPD_SendData (x_start/256);
EPD_SendData (x_start%256); //x-start
EPD_SendData (x_end/256);
EPD_SendData (x_end%256-1); //x-end

Any help is appreciated. Without fully functional partial mode, I will have stop my project.

[douglasrubims]

Same problem here.. i'm using the EPD 7in5b V2 connected to a Raspberry Pi 3B+ (using epd7in5b_V2.py)

[ChrisMenning]

I am also having trouble using partial refreshes on this display, but only when I'm writing in Python on a Raspberry Pi Zero 2 W. When I was using the same display on an ESP32 using C++, partial refreshes worked fine.