The communication interface of electronic paper display is generally divided into SPI interface and Parallel interface. The interface definition is as follows:
1. Definition of SPI interface
The necessary interfaces are BUSY, RES, D/C, CS, D0, D1. Among them D0 is the clock signal SCLK and D1 is the data signal SDIN

2. Definition of Parallel Interface
The necessary interfaces are VNEG, VGL, CLK, LE, OE, SPH, D0~D7, CPV, STV, VPOS, VGH.
Among them, VNEG, VGL, VPOS, VGH are high-voltage power supply signals, D0~D7 are data signals, and CLK, LE, OE, SPH, CPV, and STV are control signals.

1. Main difference between hardware SPI and software SPI

1) Sequence：No difference
2) SPI speed： Hardware SPI is more efficient. When writing a program, you only need to write the data to be sent to the register, and the hardware will send it automatically. The software SPI requires additional steps such as SCLK to output high and low level, data serial output and so on.

3) Hardware requirement：Hardware SPI must be supported by the processor before it can be used. Software SPI does not need specific requirements. A general IO port is OK.

 

2. Comparison of corresponding signal lines：

NameClock SignalOutput DataInput DataChip SelectionHardware SPISCKMOSIMISOSSSoftware SPIIO Analog OutputIO  Analog OutputIO  Analog InputIO  Analog Output

Electronic paper display(Epaper) is a new type of display device using micro-capsule technology and has traits like: low power consumption of refreshing, bi-stable (the last image updated can long stay on the screen even after disconnected, almost zero power consumption). However, we still need some control circuits for driving Epaper display.

Following are several ways to realize driving Epaper with low power consumption:

1. To control the Epaper to enter the deep sleep mode
In this mode, the IC data cannot be saved, and at the second time of Epaper refresh, IC needs to be reset. Generally, the current is about 5uA.

2. To control the electronic paper display to enter the standby mode In this mode, the Epaper IC data will not be lost. The IC does not need reset operation and general current is about 20uA.

3. To control the Epaper to completely power off
A hardware switch is added at the front end of the Epaper drive circuit. It is generally recommended to use P-MOS. After Epaper refreshed, first let Epaper display enter the deep sleep mode, and then directly cut off the power supply by controlling P-MOS to achieve zero power consumption.

E-paper display drive IC usually has a busy pin to tell MCU the current working state of E-paper. When E-paper display is refreshing normally, the busy pin will be in the busy state. At this time, MCU cannot read and write the IC.
Feedback from some clients reported that at the beginning of debugging, e-paper initialization is easy to get stuck in busy judgment function. Here are some possibilities for the situation:

1. SPI serial communication fails, and the IC does not work normally. At this time, the busy pin is always in the low-level state.
2. The E-paper display supply voltage is low, resulting in the IC not working normally.
3. The E-paper display FPC is inserted reversely, usually with the golden finger upward, resulting in the IC not working normally.
4. E-paper driver error. Generally, e-paper ICs are divided into SSD series and UC series. The busy status of these two ICs is reverse.
5. The busy pin is not normally connected to the circuit, resulting in the MCU always judging that busy is in the busy state.

The following is the sequence diagram of busy pin when E-paper display refreshes