SLAU893B October 2023 – July 2024 MSPM0C1103 , MSPM0C1103-Q1 , MSPM0C1104 , MSPM0C1104-Q1
The control bit CTL1.MSB defines the direction of the data input and output with most-significant-bit (MSB) or least-significant-bit (LSB) first. If the parity is enabled the parity bits is always received as last bit.
With the control register bits CTL0.DSS the bit length per transfer will be defined between 4-16 bits for Controller mode and 7-16 bits for Peripheral mode.
A transfer will be triggered with writing to the TX buffer register. The data write needs to have at least the number of bits of the transfer. For example, if only a byte is written to the TX buffer but the length of the transfer is > 8 the missing bits will be filled with 0s. On the receive path the received data will be moved to the RXFIFO or RX buffer after the number of bit defined in CTL0.DSS register have been received.
The RX and TX buffer shall be accessed with at least the bits covering one transfer.Clock polarity (CTL0.SPO) is used to control the clock polarity when data is not being transferred and it is only used in the Motorola SPI frame mode.
The SPI can be configured to work in Peripheral mode with CTL1.MS bit = 0. In Peripheral mode the clock is provided by the controller and available for the peripheral on the CLK pins which needs to be configured for input. The Clock Select and divider control bits are not used. The CS input signal is used to select/enable the data receive path of the peripheral in 4 wire mode.
The SPI can be configured to work as Controller with CTL1.MS bit = 1. In Controller mode the clock needs to be generated by selecting the available clock sources with the clock select bits. It also needs to control the CS signal depending on the selected protocol.
When setting the CTL1.PEN bit the last bit will be used as parity to evaluate the integrity of the previous bits. The CTL1.PES bit selects the parity mode as even or odd. When detecting a fault, the interrupt flag RIS.PER is set to mark the data as invalid. Parity checking is a feature to improve the robustness of the communication.