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6.14.7 Programming Examples
Example 1: The SPI controller is set as a full-duplex 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 idle at low state.
Only one byte of data to be transmitted/received in a transaction.
Uses the first 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 (SPIn_CLKDIV [8:0]) to determine the output frequency of SPI clock.
2) Write the SPIn_SSCTL register a proper value for the related settings of Master mode:
1.
Clear AUTOSS (SPIn_SSCTL[3]) to 0 to disable the Automatic Slave Selection function.
2.
Configure slave selection signal as active low by clearing SSACTPOL (SPIn_SSCTL[2])
to 0.
3.
Enable slave selection signal by setting SS (SPIn_SSCTL[0]) to 1 to activate the off-chip
slave device.
3) Write the related settings into the SPIn_CTL register to control the SPI master actions.
1.
Configure this SPI controller as master device by setting SLAVE (SPIn_CTL[18]) to 0.
2.
Force the SPI clock idle state at low by clearing CLKPOL (SPIn_CTL[3]) to 0.
3.
Select data transmitted on negative edge of SPI bus clock by setting TXNEG
(SPIn_CTL[2]) to 1.
4.
Select data latched on positive edge of SPI bus clock by clearing RXNEG (SPIn_CTL[1])
to 0.
5.
Set the bit length of a transaction as 8-bit in DWIDTH bit field (SPIn_CTL[12:8] = 0x08).
6.
Set MSB transfer first by clearing LSB (SPIn_CTL[13]) to 0.
4) Set SPIEN (SPIn_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 SPIn_TX register.
6) Waiting for SPI interrupt if the UNITIEN (SPIn_CTL[17]) is set to 1, or just polling the unit
transfer interrupt flag UNITIF (SPIn_STATUS[1]).
7) Read out the received one byte data from SPIn_RX register.
8) Go to 5) to continue another data transfer or set SS (SPIn_SSCTL[0]) to 0 to inactivate the
off-chip slave device.
Example 2: The SPI controller is set as a full-duplex 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:
Sep 9, 2019
ISD94100 Series Technical Reference Manual
Page 706 of 928
Rev1.09
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