4.3.10 - SPI Serial Communication [U3 Datasheet]

The U3 (hardware version 1.21+ only) supports Serial Peripheral Interface communication as the master only. SPI is a synchronous serial protocol typically used to communicate with chips that support SPI as slave devices.

This serial link is not an alternative to the USB connection. Rather, the host application will write/read data to/from the U3 over USB, and the U3 communicates with some other device using the serial protocol. Using this serial protocol is considered an advanced topic. A good knowledge of the protocol is recommended, and a logic analyzer or oscilloscope might be needed for troubleshooting.

There is one IOType used to write/read data over the SPI bus:

LJ_ioSPI_COMMUNICATION // Value= number of bytes (1-50). x1= array.

The following are special channels, used with the get/put config IOTypes, to configure various parameters related to the SPI bus. See the low-level function description in Section 5.2.15 for more information about these parameters:

LJ_chSPI_AUTO_CS
LJ_chSPI_DISABLE_DIR_CONFIG
LJ_chSPI_MODE
LJ_chSPI_CLOCK_FACTOR
LJ_chSPI_MOSI_PIN_NUM
LJ_chSPI_MISO_PIN_NUM
LJ_chSPI_CLK_PIN_NUM
LJ_chSPI_CS_PIN_NUM

Following is example pseudocode to configure SPI communication:

//First, configure the SPI communication.

//Enable automatic chip-select control.
AddRequest(lngHandle, LJ_ioPUT_CONFIG, LJ_chSPI_AUTO_CS,1,0,0);

//Do not disable automatic digital i/o direction configuration.
AddRequest(lngHandle, LJ_ioPUT_CONFIG, LJ_chSPI_DISABLE_DIR_CONFIG,0,0,0);

//Mode A:  CPOL=0, CPHA=0.
AddRequest(lngHandle, LJ_ioPUT_CONFIG, LJ_chSPI_MODE,0,0,0);

//Maximum clock rate (~100kHz).
AddRequest(lngHandle, LJ_ioPUT_CONFIG, LJ_chSPI_CLOCK_FACTOR,0,0,0);

//Set MOSI to FIO2.
AddRequest(lngHandle, LJ_ioPUT_CONFIG, LJ_chSPI_MOSI_PIN_NUM,2,0,0);
	
//Set MISO to FIO3.
AddRequest(lngHandle, LJ_ioPUT_CONFIG, LJ_chSPI_MISO_PIN_NUM,3,0,0);

//Set CLK to FIO0.
AddRequest(lngHandle, LJ_ioPUT_CONFIG, LJ_chSPI_CLK_PIN_NUM,0,0,0);

//Set CS to FIO1.
AddRequest(lngHandle, LJ_ioPUT_CONFIG, LJ_chSPI_CS_PIN_NUM,1,0,0);

//Execute the configuration requests.
GoOne(lngHandle);

Following is pseudocode to do the actual SPI communication:

//Transfer the data.
eGetPtr(lngHandle, LJ_ioSPI_COMMUNICATION, 0, &numBytesToTransfer, array);