Pic32 spi example


  • SPI ADC with PIC32 Harmony
  • How to Implement SPI Using PIC18F4550
  • SPI Communication with PIC microcontroller
  • PIC32 DMA SPI
  • PIC32 + RTC via SPI doesn’t work
  • PIC Microcontroller Communication with SPI Bus – XC8
  • SPI ADC with PIC32 Harmony

    Which mostly depend on how they are manufactured and how data should be flowing through the network of devices in that particular application.

    Each device is connected between 2 other devices in a circular Logically way as shown in the diagram down below. The SPI port of each slave device is designed to send data out during the second group of clock pulses an exact copy of the data it received during the first group of clock pulses.

    The whole chain acts as a communication shift register. Each slave copies the input data to the output in the next clock cycle until the SS line goes high. Such a feature only requires a single SS line from the master, rather than a separate SS line for each slave. That means a data frame will keep propagating through slave devices as long as the SS line is held low. The following diagram will show you how a single SPI master can address multiple slave devices using only one SS line.

    Independent Slave In the independent slave configuration, there is an independent slave select line for each slave. This is the way SPI is normally used. The master asserts only one chip select at a time. A typical connection diagram for a system with multiple slaves connected in the independent configuration is shown below. Which will require too many IO pins to control all SS lines. Here is a short list for the pros of SPI.

    Full-Duplex serial communication. Potentially high-speed data transfer rates can be achieved with SPI. Few wires are required for the SPI Bus typically 4 lines. Easy software configuration and setup. Extremely flexible data transfer. Very simple hardware structure.

    Transceivers are not needed unlike CAN. Disadvantages of SPI No hardware slave acknowledgment the master could be transmitting to nowhere without knowing. Typically supports only one master device.

    Requires more pins unlike I2C. No hardware-level error-checking protocol is defined. The SPI mode allows 8 bits of data to be synchronously transmitted and received simultaneously. All four modes of SPI are supported. This double-buffering of the received data SSPBUF allows the next byte to start reception before reading the data that was just received.

    This data may be irrelevant if the SPI is only a transmitter. If the interrupt method is not going to be used, then software polling can be done to ensure that a write collision does not occur. For the pins to behave as the serial port function, some must have their data direction bits in the TRISx register appropriately programmed. The master controller Processor 1 initiates the data transfer by sending the SCK signal.

    Data frame is shifted out of both shift registers on their programmed clock edge and latched on the opposite edge of the clock. Both processors should be programmed to the same Clock Polarity CKP , then both controllers would send and receive data at the same time.

    Whether the data frame is meaningful or dummy data depends on the application software. The master determines when the slave is to broadcast data by the software protocol. As each byte is received, it will be loaded into the SSPBUF register as if a normally received byte interrupts and status bits appropriately set. The clock phase and polarity are selected by appropriately programming the control bits. This then would give waveforms for SPI communication as shown in the timings diagram down below.

    How to Implement SPI Using PIC18F4550

    This communication protocol is basically a Master — Slave implementation where the master device controls the clock based on which the slave devices operate. The master communicates with a slave or a number of slaves in a system through the SPI bus. The SPI is a full-duplex high speed communication protocol. The master and slave can transmit and receive data at the same time.

    The master is the device which generates clock for all these data transmissions. Read PIC microcontroller tutorial based on PIC18F microcontrollers in which one of the microcontroller acts as a slave transmitter and the other acts as master receiver. With the help of an LCD, this particular project demonstrates the complete data transfer between a master and slave when both the master and slave are transmitting and receiving the data at the same time.

    The above diagram is a single buffer implementation of the SPI hardware. The only difference in the hardware configuration of a master and slave device is the direction of the clock. For a master device the clock is always output and for a slave device the clock is always input. The Clock unit can generate the clock required for the data transmission.

    In case of a master device the clock is generated by the device and all other devices in the SPI bus send or receive data to the master based on this clock. When the microcontroller is configured as a slave it can only accept the clock from a master device. After the eighth clock since the communication starts, one byte of data has been shifted out through the SDO and one byte of data has been shifted in through the SDI. Now the SISO has an entire byte received from the slave while transmitting a byte to the slave.

    In case of a slave device this register holds the SPI data which needed to be shifted out to the master or which has been shifted in from the master. The first two bits and the last bit of this register are only dedicated for the SPI communication.

    All the bits of these register are significant and should be carefully set them. The CKP bit is used to decide which are the idle state and the active state of the clock. Read PIC microcontroller tutorial to know more. To have clear understanding of code writing visit PIC Microcontroller tutorial.

    It also set the clock polarity and when to sample input data and to transmit output data regarding the clock transition states. It also sets the SPI pins as input or output as required by the master. It can also disable all other modules multiplexed into the SPI pins. It also sets the SPI pins as input or output as required by the slave. The master first write the data and then wait for the data to complete transmission and then read the received data while the slave first wait till all the data bits has been received, and then reads the data followed by a data write.

    The functions are explained with more details in PIC microcontroller tutorial. The slave then transmits the same data which it has received back to the master which is then displayed in the second line of LCD.

    In this way the master is doing transmission and reception and the slave is also performing transmission and reception.

    SPI Communication with PIC microcontroller

    A typical connection diagram for a system with multiple slaves connected in the independent configuration is shown below. Which will require too many IO pins to control all SS lines. Here is a short list for the pros of SPI. Full-Duplex serial communication. Potentially high-speed data transfer rates can be achieved with SPI. Few wires are required for the SPI Bus typically 4 lines. Easy software configuration and setup.

    Extremely flexible data transfer. Very simple hardware structure. Transceivers are not needed unlike CAN. Disadvantages of SPI No hardware slave acknowledgment the master could be transmitting to nowhere without knowing. Typically supports only one master device.

    PIC32 DMA SPI

    Requires more pins unlike I2C. No hardware-level error-checking protocol is defined. The SPI mode allows 8 bits of data to be synchronously transmitted and received simultaneously. All four modes of SPI are supported.

    This double-buffering of the received data SSPBUF allows the next byte to start reception before reading the data that was just received. This data may be irrelevant if the SPI is only a transmitter. If the interrupt method is not going to be used, then software polling can be done to ensure that a write collision does not occur. The master and slave can transmit and receive data at the same time.

    The master is the device which generates clock for all these data transmissions. Read PIC microcontroller tutorial based on PIC18F microcontrollers in which one of the microcontroller acts as a slave transmitter and the other acts as master receiver. With the help of an LCD, this particular project demonstrates the complete data transfer between a master and slave when both the master and slave are transmitting and receiving the data at the same time.

    The above diagram is a single buffer implementation of the SPI hardware.

    PIC32 + RTC via SPI doesn’t work

    The only difference in the hardware configuration of a master and slave device is the direction of the clock. For a master device the clock is always output and for a slave device the clock is always input.

    The Clock unit can generate the clock required for the data transmission. In case of a master device the clock is generated by the device and all other devices in the SPI bus send or receive data to the master based on this clock.

    PIC Microcontroller Communication with SPI Bus – XC8

    When the microcontroller is configured as a slave it can only accept the clock from a master device. After the eighth clock since the communication starts, one byte of data has been shifted out through the SDO and one byte of data has been shifted in through the SDI.

    Now the SISO has an entire byte received from the slave while transmitting a byte to the slave. In case of a slave device this register holds the SPI data which needed to be shifted out to the master or which has been shifted in from the master. The first two bits and the last bit of this register are only dedicated for the SPI communication.


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