March 13, 2025

STM32F429 Discovery Kit - LCD - the schematic

Reading through some of the sources I have learned that two different ways are provided to access this thing. One is via an SPI device -- this is simpler perhaps, but slow. The other way is via a bus interface. I have also read that the FSMC (static memory controller) on the F429 is used, no doubt in some way to access the bus interface. The FSMC is also used to access the static ram on the discovery board, so I will be dealing with that thing sooner or later.

The disco schematic shows a device STMPE811QTR at i2c address 1000001. This is described as a 4 wire resistive touch screen sensor. The 4 wires seem to be XL, XR, YD, YU for left/right, up/down. A 66 page datasheet is available.

The same page of the schematic shows FRD240C48003-B Searching on this leads me to a 20 page document "FRIDA_LCD_FRD240C48003-B.pdf". This is dated 2019 and describes a TFT-LCD module.

One page is particularly valuable as it lists all the signals on what must be a 48 pin connector/cable.

It shows parallel data for RGB. Each gets 6 bits. So 18 GPIO signals from the F429 get used to drive these. You can work out which these are with a bit of effort and searching on the disco schematic. The pins seem to be selected entirely at random.

There are 4 signals (IM0,1,2,3) that the "FRIDA" document says select the interface mode. The disco board sets these to 0110. A table in the FRIDA document gives all 16 possibilites, but 0110 is "4 wire 8-bit data serial I (SDA in/out)

pin 37 is the serial clock, pin 30 is SDA in/out. We also get a CS (chip select) signal. These are driven by various GPIO pins from the F429.

Reset to the LCD is driven by NRST, the system reset.

Feedback? Questions? Drop me a line!

Tom's Computer Info / tom@mmto.org