Project Logs

Collapse

• Working with the screen

  Matthew • 08/01/2026 at 10:57 • 0 comments

  Without this forum post, I never would have gotten this far. Sincere thanks to Simbarashe Bryne Chipembe because their set of init commands really helped me figure things out. To understand why their init sequence mattered, let's take a look at the pinout for the display itsef. (I mostly copy/pasted this from the datasheet, so any English mistakes may have been carried over)
  

  Pin number	Name	Description
  1	GND
  2	IOVCC	I/O POWER 1.8V/2.8V(typ)
  3	VCC	POWER 2.8V-3.0V
  4	CS	Chip select signal. Amplitude: IOVCC-GND Low: the driver is selected and accessible High: the driver is not selected and not accessible. Tie to IOVCC when not in use
  5	RS	Register select signal.Amplitude: IOVCC-GND Low: select Index register High: select control register. Tie to IOVCC when not in use
  6	WR	Write strobe signal in 80-system bus interface operation and enables write operation when WRX is low. Synchronous clock signal (SCL) in serial interface operation. Amplitude: IOVCC-GND. Tie to IOVCC when not in use
  7	RD	Read strobe signal in 80-system bus interface operation and enables read operation when RDX is low. Amplitude: IOVCC-GND. Tie to IOVCC when not in use
  8	DB0	16-bit parallel bi-directional data bus for 80-system interface operation (Amplitude: IOVCC-GND). 16-bit I/F: DB15-DB0 are used. 8-bit I/F: DB15-DB8 are used.
  9	DB1	"
  10	DB2	"
  11	DB3	"
  12	DB4	"
  13	DB5	"
  14	DB6	"
  15	DB7	"
  16	DB8	"
  17	DB9	"
  18	DB10	"
  19	DB11	"
  20	DB12	"
  21	DB13	"
  22	DB14	"
  23	DB15	"
  24	RESET	Reset pad. Initializes the IC when it is low. Must be reset after power-on.
  25	LCM_ID	reserved (not sure what it's reserved for)
  26	GND
  27	IM0	Select a mode to interface to host processor. (Amplitude: IOVCC ~GND) IM0: LOW,80-system 16-bit interface IM0: HIGH,80-system 8-bit interface
  28	NC/FMARK	reserved
  29	VCI	POWER 2.8V-3.0V
  30	LEDK4	LED Cathode
  31	LEDK3	LED Cathode
  32	LEDK2	LED Cathode
  33	LEDK1	LED Cathode
  34	LEDA	LED Anode
  35	YU/NC	Not connected but would be for the touch panel
  36	XL/NC	Not connected but would be for the touch panel
  37	YD/NC	Not connected but would be for the touch panel
  38	XR/NC	Not connected but would be for the touch panel

  The ILI9335 driver is a chip on the display's FPC connector that then breaks out to the individual pins in the LCD matrix. The pins above are just the ones exposed from the ILI9335 driver to the FPC connector and on to the dev board. To replicate the dev board, I needed to connect to these pins. 

  The dev board pulled IM0 low, so it was a 16-bit interface. I wired the pins up to the pico the same way the dev board was wired up. Though, the DB0-15 pins were wired in order so I could try using pio (more on that later).

  The 16-bit interface works like this when writing:

  1. Flip CS to low

  2. Flip RS to low (because we're writing to the index registers)

  3. Keep RD high

  4. Flip WR to low

  5. Set the bits for DB0-15. The first set of bits will be the index registers

  6. Set WR to high

  7. Set RS to high (Index registers are written, so this is now high)

  8. (short wait)

  9. Set WR to low

  10. Set the bits for DB0-15. This second set of bits are the data registers

  11. Set WR to high

  12. Set CS to high 

  Done.

  So how does this relate to the init code from that forum post? Well, every time they ran their `WRITE_LCD_REG` function, they specified the register and the data to write. I read through the datasheet multiple times but for some reason, reading those lines finally clicked for me.

  
  Let's take the first command, `WRITE_LCD_REG(0x01, 0x0100);`

  This would mean we do the following:

  1. Flip CS to low

  2. Flip RS to low

  3. Maintain RD as high

  4. Flip WR to low

  5. Set pins DB0-15 to be 0000 0000 0000 0001

  6. Set WR to high

  7. Set RS to high

  8. Wait 10ns or so

  9. Set WR to low

  10. Set the bits for the data, which is now: 0000 0001 0000 0000

  11. Set WR to high

  12. Set CS to high

  Then I just compared their data to the ILI9335 datasheet I got from the Aliexpress seller and was able to configure the display. When I wanted to write to certain sections...

  Read more »

View project log