SPI

• The SPI port runs directly to the Pi Pico microcontroller.  The buffers are activated only when the Pi Pico addresses CE1/.

• All 4 clock/data modes are supported

• Choice of 12 speeds, 7.6KHz to 15.6MHz

• Active-low Slave Select line for 4-wire operation

• 3.3V logic drivers with 91 ohm in series to match cable impedance.

• 3.3V logic receiver on MISO with a 1 Mohm pulldown.

• This example uses the 23S17 I/O Expander with two 8-bit bytes.

• Row 1 writes 0 to register 0 using device address 0x40. This programs all 8 bits of the first byte as outputs.

• Row 2 writes the data, 0x55 in this case, to register 0x12.

• Row 3 and 4 execute simultaneously as a "Write/Read". The device address is now written as 0x41, with the lsb indicating a read operation. Register 0x12 is again chosen. The last byte written, the 0, is just a place holder in Row 3. The output Read Data in Row 4.

• In Rows 3 and 4, there are 24 clock pulses, with Row 3 writing the its data on MOSI, and Row 4 reading the last byte from MISO.

API (Application Programming Interface:

C API:

void init_SPI(int baudrate, int mode);

void write_SPI(uint8_t *write_data);

void read_SPI(int num_read_bytes, uint8_t *rd_buf);

void write_read_SPI(uint8_t *write_data, uint8_t *rd_buf);

PYTHON API:

init_spi(baudrate, mode)

write_spi(spi_list)

read_spi(num_read_bytes)

write_read_spi(write_data)