Overview

This is a 4.2inch e-Paper display module for Raspberry Pi Pico, 400 x 300 pixels, support black, white, and 4 grayscale display, SPI interface.

Features

No backlight, keeps displaying last content for a long time even when power down.
Ultra-low power consumption, basically power is only required for refreshing.
SPI interface, requires minimal IO pins.
Onboard voltage translator, compatible with 3.3V / 5V MCUs.
2 x user buttons for easy interacting.

Specification

Size: 4.2 inch
Outline dimensions (bare screen): 90.1mm × 77.0mm × 1.18mm
Outline dimensions (driver board): 93.5mm × 78.5mm
Display size: 84.8mm x 63.6mm
Operating voltage: 3.3V/5V
Communication interface: SPI
Pitch: 0.212 x 0.212
Resolution: 400 x 300
Display color: Black, White
Greyscale: 4
Full refresh: 4s
Refreshing power: 26.4mW(typ.)
Sleep current: <0.01uA (almost 0)

Note: Refresh time: refresh time for the experimental test data, the actual refresh time will be inaccurate, subject to the actual effect. The global refresh process will have a flickering effect, this is a normal phenomenon.
Power consumption: power consumption data for the experimental test data, the actual power consumption due to the existence of the driver board, and the actual use of different circumstances, there will be a certain error, subject to the actual effect.

SPI Timing

Note: Different from the traditional SPI protocol, the data line from the slave to the master is hidden since the device only has a display requirement.

CS is a slave chip select, when CS is low, the chip is enabled.
DC is data/command control pin, when DC = 0, write command, when DC = 1, write data.
SCLK is the SPI communication clock.
SDIN is the data line from the master to the slave in SPI communication.
Timing: CPHL=0, CPOL=0 (SPI0)

【Note】: for more details about SPI communication, you can search on the Internet.

Working protocoal

Pixel & Byte

We define the pixels in a monochrome picture, 0 is black and 1 is white.
White：□: Bit 1
Black：■：Bit 0

The dot in the figure is called a pixel. As we know, 1 and 0 are used to define the color, therefore we can use one bit to define the color of one pixel, and 1 byte = 8pixels
For example, If we set the first 8 pixels to black and the last 8 pixels to white, we show it by codes, they will be 16-bit as below:

For the computer, the data is saved in MSB format:

So we can use two bytes for 16 pixels.

In addition to bicolor displaying, the 3.7inch e-Paper also supports four grayscale.

To display grey pixels, we need to define data for gray

Black: 00b
Dark Grey: 01b
Light Grey: 10b
White: 11b

Pixel	1		2		3		4		5		6		7		8
Bit	7	6	5	4	3	2	1	0	7	6	5	4	3	2	1	0
Data	0	0	0	0	0	1	0	1	1	0	1	0	1	1	1	1
Color	Black		Black		Dark Grey		Dark Grey		Light Grey		Light Grey		White		White
Byte	0x05								0xAF

The display divides a four-grayscale picture into two pictures. The pixels in the same position of pictures are combined into one pixel.

Register	White	Light Grey	Dark Grey	Black
0x10	0x01	0x01	0x00	0x00
0x13	0x01	0x00	0x01	0x00

With the tables above, you can define the data which can be used to display grayscale pixels in the 3.7inch e-Paper

Pixel	1		2		3		4		5		6		7		8
Bit	7	6	5	4	3	2	1	0	7	6	5	4	3	2	1	0
Data	0	0	0	0	0	1	0	1	1	0	1	0	1	1	1	1
Color	Black		Black		Dark Grey		Dark Grey		Light Grey		Light Grey		White		White
Byte	0x05								0xAF
Bit in 0x10 register	0	0	0	0	0	0	0	0	0	1	0	1	0	1	0	1
Bit in 0x13 register	0	0	0	0	0	1	0	1	0	0	0	0	0	1	0	1
Data sent to 0x10 register	0x00								0x55
Data sent to 0x13 register	0x05								0x05

Navigation menu

Template: Pico e-Paper 4.2 Spec

Contents