Problem of LCD connection with ESP32 pins, which are supported flash?

[thienluan]

At the first stage, I connected my LCD to ESP32 with GPIO25, GPU26, GPIO27, GPIO18, and GPIO23 as in the below figure. And it worked very well.

issue 1

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Unfortunately, this group of GPIO (25, 26, 27, 28, 23) are now busy with other connection. Then I tried to connect my LCD with group GPIO (11, 10 ,6 ,7) as in the below figure. But it did not work.

issue 2

isssue1.jpg (26.75 KiB) Viewed 5452 times

I know that these pin are support for communicate with internal/external flash, and are not recommended for other uses. However, I have a little confusion about this sentence. These pins are just only used for connecting with flash or they can be configured to use for other purposed.
Please help to check my problem.

[ESP_Angus]

Hi thienluan,

I'm assuming you're using an ESP32-D0 (or a WROOM module) and not an ESP32-D2 or an ESP32-D4-PICO in this reply.

I know that these pin are support for communicate with internal/external flash, and are not recommended for other uses. However, I have a little confusion about this sentence. These pins are just only used for connecting with flash or they can be configured to use for other purposed.

For most intents and purposes, these pins can't be reused. They are the reason your code no longer works.

You may be able to reuse SD_DATA_2 and SD_DATA_3 (GPIOs 9 & 10) if you compile and flash your app in DIO or DOUT mode, not QIO or QOUT. Your app will boot and run a little slower in this configuration.

For people who are very careful, experienced, and patient, it should be technically possible to reuse the other SPI bus pins (GPIOs 6,7,8) that are connected to the SPI flash in order to connect to some other SPI device (adding a new CS pin and a different GPIO). There isn't any support for this in ESP-IDF's SPI drivers (it's difficult because all of the code which accesses the other SPI device has to run from IRAM with the flash disabled). However it should be technically possible if you wrote the code from scratch, which is why the datasheet says "recommended". Even then, you have to be careful about the signal integrity of these pins if you wire them to other boards.

Angus

[thienluan]

Hi Angus,

Firstly, thank you very much for your quick response. Your answer gave a big help to me.

I really want to you LCD with these pins because other pins are fully busy in my design.

Therefore, I have a small question about this topic. Is there any difference if I use ESP32-D2 or ESP32-D4-PICO? Because ESP32-D2 has an internal flash. So, in some cases, we can disable the pins from connecting to flash. Then, we can use them for other purposes.

Thank you,