Template: Pico e-Paper 2.66-B Spec
Overview
2.66inch E-Paper E-Ink Display Module For Raspberry Pi Pico, 296×152 Pixels, Black / White /Red, 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
Specification
- Operating voltage: 3.3V/5V
- Interface:3-wire SPI, 4-wire SPI
- Outline dimensions (Driver board): 74.0mm × 37.5mm
- Outline dimensions (raw panel): 71.820mm × 36.304mm × 1.05mm
- Display size: 60.088mm × 30.704mm
- Dot pitch: 0.202 × 0.203mm
- Resolution: 296×152 pixels
- Display color: Black, white, red
- Greyscale: 2
- full refresh time: 15s
- Refresh power: 42.4mW(typ.)
- Standby current: <0.01uA(almost 0)
- Viewing Angle: >170°
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 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.
SPI communication has data transfer timing, which is combined by CPHA and CPOL.
- CPOL determines the level of the serial synchronous clock at an idle state. When CPOL = 0, the level is Low. However, CPOL has little effect on transmission.
- CPHA determines whether data is collected at the first clock edge or at the second clock edge of the serial synchronous clock; when CPHL = 0, data is collected at the first clock edge.
- There are 4 SPI communication modes. SPI0 is commonly used, in which CPHL = 0, CPOL = 0.
As you can see from the figure above, data transmission starts at the first falling edge of SCLK, and 8 bits of data are transferred in one clock cycle. Here, SPI0 is in used, and data is transferred by bits, MSB first.
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 computer, the data is saved in MSB format:
So we can use two bytes for 16 pixels.
For e-paper B, the display colors are red, black, and white. We need to split the picture into 2 pictures, one is the black and white picture, another is the red and white picture. When transmitting, because one register controls a black or white pixel, one controls Red or white display. The black and white part of the display uses 1 byte to control 8 pixels, and the red and white part use 1 byte to control 8 pixels.
For example, suppose there are 8 pixels, the first 4 are red, and the back 4 are black:
They need to be disassembled into a black and white picture and a red and white picture. Both pictures have 8 pixels, but the first four pixels of the black and white picture are white, the last 4 pixels are black, and the first 4 pixels of the red and white picture One pixel is red, and the last four pixels are white.
If you define that the data of white pixel is 1 and the black is 0, then we can get:
So that we can use 1 byte to control every eight pixels.
