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6.16.7 Programming Examples
Example 1:
The SPI controller is set as a master to access an off-chip slave device with the
following specifications:
Data bit is latched on positive edge of SPI bus clock.
Data bit is driven on negative edge of SPI bus clock.
Data is transferred from MSB first.
SPI bus clock is low at idle state.
Only one byte of data to be transmitted/received in a transaction.
Uses the SPI slave select pin to connect with an off-chip slave device. The slave selection
signal is active low.
The operation flow is as follows:
1) Set DIVIDER (SPI_CLKDIV[7:0]) to determine the output frequency of SPI clock.
2) Write the SPI_SSCTL register a proper value for the related settings of Master mode:
1. Clear AUTOSS (SPI_SSCTL[3]) to 0 to disable the Automatic Slave Selection function.
2. Configure slave selection signal as active low by clearing SSACTPOL (SPI_SSCTL[2])
to 0.
3. Enable slave selection signal by setting SS (SPI_SSCTL[0]) to 1 to active the off-chip
slave device.
3) Write the related settings into the SPI_CTL register to control the SPI master actions.
1. Configure this SPI controller as master device by setting SLAVE (SPI_CTL[18]) to 0.
2. Force the SPI clock to low at ilde state by clearing CLKPOL (SPI_CTL[3]) to 0.
3. Select data transmitted on negative edge of SPI bus clock by setting TXNEG
(SPI_CTL[2]) to 1.
4. Select data latched on positive edge of SPI bus clock by clearing RXNEG (SPI_CTL[1])
to 0.
5. Set the bit length of a transaction as 8-bit in DWIDTH bit field (SPI_CTL[12:8] = 0x08).
6. Set MSB transfer first by clearing MSB (SPI_CTL[13]) to 0.
4) Set SPIEN (SPI_CTL[0]) to 1 to enable the data transfer with the SPI interface.
5) If this SPI master attempts to transmit (write) one byte data to the off-chip slave device, write
the byte data that will be transmitted into the SPI_TX register.
6) Waiting for SPI interrupt if the UNITIEN (SPI_CTL[17]) is set to 1, or just polling the unit
transfer interrupt flag UNITIF (SPI_STATUS[1]).
7) Read out the received one byte data from SPI_RX register.
8) Go to 5) to continue another data transfer or set SS (SPI_SSCTL[0]) to 0 to inactivate the off-
chip slave device.
Example 2:
The SPI controller is set as a slave device and connects with an off-chip master
device. The off-chip master device communicates with the on-chip SPI slave controller through
the SPI interface with the following specifications:
