ILI9488 MISO Fault Question

Author	Message
stanleyella Guru Joined: 25/06/2022 Location: United Kingdom Posts: 2252	Posted: 10:27pm 29 Nov 2022         phil99 said   Ok that proves the touch chip has not been damaged, it was just interference from LCD_SDO preventing touch working. Blit, Pixel() and Save Image cannot work while LCD_SDO is disconnected. That is the pin that sends data from the screen to the Pico. The problem is three outputs (LCD_SDO, T_DO & SD_DO) must share one input (MISO). For that to work only one can be active at a time, and the faulty LCD_SDO is always active. The reason for the 680R or transistor or diode circuits is to provide enough isolation from LCD_SDO to allow touch and SD to work but still allow LCD_SDO to access MISO. Perhaps the fault on your panel is different. Measure the voltage between LCD_SDO and Gnd. (with nothing else connected to that pin) and let me know what it is. Mine is close to 0V. How the diode switching is supposed to work:- With LCD_SDO low and LCD_CS high the diode is reverse biased, isolating LCD_SDO from MISO so touch or SD should be able to send data to MISO. When the Pico wants data from the screen the Pico pulls LCD_CS low (the other two CS pins are high keeping Touch and SD off). This allows the diode to be forward biased so LCD_SDO can send data to MISO. When screen data sends LCD_SDO high (and LCD_CS is low) it goes through the diode to MISO. When screen data sends LCD_SDO low (and LCD_CS is low) the resistor pulls MISO low. . great info but same problems but only tried 680R and the diode/10KR It is either graphics including blit but no touch or working touch, sd card and graphics but no blit... which I had never thought would be affected. If I can not get it to work like ili9341 then do I need blit? would gui dials be affected? I can not get it to do blit even after option reset and resetting everything, what an interesting display. Not boring like ili9341 which works. Edited 2022-11-30 09:32 by stanleyella