README.md

RP2040-LCD example of Pico-examples revisited.

Taken from the Pico-examples, and expanded

• RP2040 with two 74HC595 daisy-chained to drive TFT LCD of 8080 MCU 16-bit bus interface, which can save a lot of pins.
• The 74HC595 is an 8-bit serial-in, serial or parallel-out shift register with output latches. The have 100 MHz (typical) shift out frequency.

Expanded with:

• Two shift register 74HC595 daisy chained together to save many pins, which is main purpose of this project.
• Simultaneously drive two LCDs with different interfaces.
• Use 74HC165 (PISO) to read from LCD.
• Also supports GPIO shift of bit-banging method output to drive LCD.

Supported and tested TFT screens

Logic probe timing diagram

• LCD control command

• Pixels data of BGR565 after 0x2C.

Circuit Diagram Table

RP2040	74HC565N(1)	74HC565N(2)	3.2 inch 16bit	2.8 inch SPI
GPIO0	DS			SDI(MOSI)
GPIO1	SHCP	SHCP		SCK
GPIO2			RS	DC
GPIO3			WR
GPIO4			RESET	RESET
GPIO5	STCP	STCP
VCC	VCC	VCC
VCC	MR	MR
GND	GND	GND	GND	GND
GND/GPIO3	OE	OE
	Q7S	DS
	Q0		D00
	Q1		D01
	Q2		D02
	Q3		D03
	Q4		D04
	Q5		D05
	Q6		D06
	Q7		D07
		Q0	D08
		Q1	D09
		Q2	D10
		Q3	D11
		Q4	D12
		Q5	D13
		Q6	D14
		Q7	D15
VCC	VCC	VCC	VCC	VCC
VCC				BL(High Act)
VCC			RD
GND			CS	CS
GND			BL(Low Active)

Second Stage, 74HC595 with 74HC165

SIPO and PISO

• The below tested that 74HC595 with 74HC165 direct communication, send data to 74HC595 and read same data from 74HC165.

static inline uint8_t lcd_74hcxxx_test(uint8_t data) {
    uint8_t bitOrder = MSBFIRST;
    uint8_t value = 0;
    uint8_t i;

    gpio_put(PIN_LATCH, 0);
    for (i = 0; i < 8; ++i) {
        if (bitOrder == MSBFIRST) {
            gpio_put(PIN_DOUT, (data & (1 << (7 - i))) >> (7 - i));
        } else {
            gpio_put(PIN_DOUT, (data & (1 << i)) >> i);
        }
        gpio_put(PIN_CLK, 1);
        gpio_put(PIN_CLK, 0);
    }
    gpio_put(PIN_LATCH, 1);
    gpio_put(PIN_PL, 0);
    sleep_us(1);
    gpio_put(PIN_PL, 1);
    sleep_us(1);
    for (i = 0; i < 8; ++i) {
        gpio_put(PIN_CP, 0);
        if (bitOrder == LSBFIRST)
            value |= gpio_get(PIN_DIN) << i;
        else
            value |= gpio_get(PIN_DIN) << (7 - i);
        gpio_put(PIN_CP, 1);
        sleep_us(1);
    }
    static char text[64];
    sprintf(text, "TEST Read 74hcxxx , 0x%04x\r\n", value);
    uart_puts(UART_ID, text);
    return value;
}

Read ILI9341 device ID

RP2040	74HC565N(1)	74HC565N(2)	3.2 inch 16bit	74HC165D
GPIO0	DS
GPIO1	SHCP	SHCP
GPIO2			RS
GPIO3			WR
GPIO4			RESET
GPIO5	STCP	STCP
VCC	VCC	VCC
VCC	MR	MR
GND	GND	GND	GND	GND(08)
GND	OE	OE
	Q7S	DS
	Q0		D00	D00(11)
	Q1		D01	D01(12)
	Q2		D02	D02(13)
	Q3		D03	D03(14)
	Q4		D04	D04(03)
	Q5		D05	D05(04)
	Q6		D06	D06(05)
	Q7		D07	D07(06)
		Q0	D08
		Q1	D09
		Q2	D10
		Q3	D11
		Q4	D12
		Q5	D13
		Q6	D14
GPIO12				Q7(09)
GPIO13			RD
GPIO14				CP(02)
GPIO15				PL(01)
VCC	VCC	VCC	VCC	VCC
GND			CS
GND			BL(Low Active)

• 

Enable XPT2046 and use SPI

RP2040	2.8 inch SPI	XPT2046
GPIO3	SDI(MOSI)	SDI(MOSI)
GPIO2	SCK	SCK
GPIO0	DC
GPIO4	SDO(MISO)	SDO(MISO)
GPIO5	CS
GPIO1	RESET
GPIO8		CS
VCC	BK
VCC	VCC
GND	GND

• Added LVGL examples

Third Stage， Draw the PCB adapter board

• First of all, I would like to thank www.jiepei.com/ company for supporting PCB sample production, including shipping costs. Its free sample promotion is very good for people who like DIY electronic products.

• Runing lv_demo_benchmark on lvgl v9.1

Shortcomings

• This project needs addidtional ICs and complex wiring. The 74HC595 and 74HC165 can only work in the bit-banging method with fixed clock_freq, also in shiftout need an extra instruction to delay, otherwise will show black screen. When tested in the PIO method, the LCD screen is block.I think it may be that the MCU is too fast and produces noise signal interference, Or violates the timing specification. At the moment I don't have enough experience in this area, maybe in the future I'll spend some time making it flexible and robust.