Waveshare e-Paper - Page 10

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User Manual
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Note 5-5: This pin (BS0) is for 3-line SPI or 4-line SPI selection. When it is “Low”, 4-line SPI is selected.
When it is “High”, 3-line SPI (9 bits SPI) is selected. Please refer to below Table:
Table: Bus Interface Selection
BS1 State
MCU Interface
L
4-line serial peripheral interface (SPI)
H
3- line serial peripheral interface (SPI) - 9 bits SPI