SPI (Serial Peripheral Interface) is a common communication protocol used in embedded systems and electronic devices. If you’re preparing for an interview for a position that involves working with SPI, it’s important to be familiar with the technical aspects of the protocol. Here are some common SPI protocol interview questions and answers that can help you prepare. Knowing these typical SPI protocol interview Q&As can boost your chances of acing an SPI-related job interview. You can also check our comprehensive guide on “I2C Interview Questions” and “Difference between I2C and SPI”.
The most commonly asked “SPI Protocol Interview Questions and Answers”
Q1) What is SPI Protocol?
SPI, short for Serial Peripheral Interface, is a full-duplex, synchronous serial communication protocol that facilitates data exchange between a master device and multiple peripheral devices. It employs a master-slave architecture, allowing the master to initiate data transfer and control the communication with the connected peripherals.
SPI typically involves four communication lines:
a. MISO (Master In, Slave Out)
b. MOSI (Master Out, Slave In)
c. SCLK (Serial Clock)
d. SS/CS (Slave Select/Chip Select)
The master device generates the clock signal (SCLK) to synchronize data transfer, while the slave devices respond accordingly. This protocol enables high-speed communication with a minimal number of wires, making it an efficient choice for connecting devices within the same circuit.
Q2) How Does SPI Protocol Work?
SPI communication follows a sequential process initiated by the master device. Here’s a step-by-step breakdown:
a. Slave Selection: The master activates the SS/CS line for the specific slave device it intends to communicate with, ensuring that only that slave responds.
b. Clock Generation: The master generates clock pulses (SCLK) to synchronize data transmission. The frequency of the clock is determined by the system’s requirements.
c. Data Transmission (MOSI): The master sends data to the selected slave through the MOSI line, while simultaneously, the slave sends data back to the master through the MISO line.
d. Data Reception (MISO): The master reads data from the MISO line during the same clock cycle it transmits data to the slave.
e. Slave Deactivation: After data exchange, the master deactivates the SS/CS line, signaling the end of communication with the specific slave.
Q3) What are the Advantages of SPI Protocol?
SPI protocol offers several advantages, making it a popular choice in embedded systems:
a. High Speed: SPI supports high-speed data transfer, making it suitable for applications that demand quick and efficient communication.
b. Simple Implementation: With its minimalistic four-wire configuration, SPI is relatively easy to implement, reducing the complexity of the overall system.
c. Full-Duplex Communication: SPI allows simultaneous data transmission and reception, enhancing communication efficiency between the master and slave devices.
d. Multiple Slave Devices: The master device can communicate with multiple slave devices on the same bus, providing scalability and flexibility in system design.
e. Versatility: SPI is versatile and can be adapted to various applications, including sensors, displays, memory devices, and more.
Q4) What are the 4 modes of SPI?
The four modes of SPI (Serial Peripheral Interface) are defined by the clock polarity (CPOL) and clock phase (CPHA). The modes are:
- Mode 0: CPOL=0, CPHA=0
- Mode 1: CPOL=0, CPHA=1
- Mode 2: CPOL=1, CPHA=0
- Mode 3: CPOL=1, CPHA=1
Q5) What are the 4 lines of SPI?
The four lines of SPI are:
- MISO (Master In, Slave Out)
- MOSI (Master Out, Slave In)
- SCLK (Serial Clock)
- SS/CS (Slave Select/Chip Select)
Q6) What is the use of SPI protocol?
The SPI protocol facilitates synchronous serial communication between a master device and one or more peripheral devices. It is widely utilized in embedded systems, sensor networks, memory devices, displays, and diverse applications that demand high-speed and efficient data transfer.
Q7) What are the two types of SPI?
The two types of SPI are:
- 3-Wire SPI: Uses MISO, MOSI, and SCLK lines (without a dedicated SS/CS line).
- 4-Wire SPI: Includes MISO, MOSI, SCLK, and SS/CS lines for full-duplex communication and multiple slave device support.
Q8) What is the maximum speed of SPI?
The maximum speed of SPI depends on the capabilities of the devices involved. It can range from a few kilobits per second to several megabits per second.
Q9) Which SPI mode is best?
The choice of the best SPI mode depends on the specific requirements of the application. There is no universally “best” mode; it varies based on factors like data integrity, clock polarity, and phase requirements.
Q10) What is SPI frequency?
SPI frequency, also referred to as clock frequency, denotes the rate at which data traverses the SPI bus. Measured in hertz (Hz), it establishes the pace of communication between the master and slave devices.
Q11) Is SPI faster than UART?
Yes, SPI is generally faster than UART. SPI operates in full-duplex mode and supports higher clock frequencies, leading to faster data transfer compared to the asynchronous communication of UART.
Q12) What is the baud rate of SPI?
Unlike UART, SPI does not have a fixed baud rate. The communication speed in SPI is determined by the clock frequency (SCLK) set by the master device.
Q13) Why SPI is full-duplex?
is full-duplex because it allows simultaneous transmission and reception of data. This is achieved by having separate lines for data sent from the master to the slave (MOSI) and from the slave to the master (MISO), enabling bidirectional communication.
Q14) How to test SPI interface?
SPI interfaces can be tested using a variety of methods, including oscilloscopes to observe signal waveforms, logic analyzers for detailed protocol analysis, and connecting the devices in a controlled environment to verify proper data exchange.
Q15) Is SPI bidirectional?
Yes, SPI is bidirectional. It supports two-way communication, allowing data to be transmitted from the master to the slave (MOSI) and from the slave to the master (MISO) simultaneously.
Q16) Which is faster I2C or SPI?
SPI is generally faster than I2C due to its synchronous nature and the absence of a shared data line, allowing for higher clock frequencies.
Q17) What determines SPI speed?
SPI speed is determined by the clock frequency (SCLK) set by the master device. The higher the clock frequency, the faster the data transfer rate.
Q18) What is SPI voltage?
SPI operates with various voltage levels, and the voltage is determined by the specific devices connected on the bus. Common voltage levels include 3.3V and 5V.
Q19) How many wires are there in SPI?
SPI typically uses four wires: MISO, MOSI, SCLK, and SS/CS. However, in 3-Wire SPI, the SS/CS line may be omitted.
Q20) How many pins does SPI use?
SPI commonly uses four pins: MISO, MOSI, SCLK, and SS/CS. The number of pins may vary depending on the specific implementation and requirements.
Q21) Why SPI has 4 modes?
The four modes of SPI accommodate different clock polarities and phases, providing flexibility to suit various device communication requirements and ensuring compatibility with diverse hardware configurations.
Q22) Is SPI synchronous?
Yes, SPI is synchronous. Synchronization of data transmission in SPI occurs through a clock signal (SCLK) generated by the master device, guaranteeing precise timing coordination between the communicating devices.
Q23) What is 3 wire SPI?
3-Wire SPI is a simplified version of the SPI protocol that omits the dedicated SS/CS line. It uses MISO, MOSI, and SCLK lines for communication.
Q24) What is the SPI format?
The SPI format is defined by the chosen mode (Mode 0, Mode 1, Mode 2, or Mode 3) and includes specifications for clock polarity (CPOL) and clock phase (CPHA) to determine when data is sampled and shifted.
Q25) What are the advantages of SPI?
Advantages of SPI include high-speed communication, simplicity in implementation, support for multiple slave devices, and full-duplex operation.
Q26) What are the disadvantages of SPI?
Disadvantages of SPI include potential signal integrity issues over long distances, increased wiring complexity with multiple devices, and the lack of a standardized protocol across all manufacturers.
Q27) Should I use SPI?
The decision to use SPI depends on the specific requirements of your application. SPI is a suitable choice for high-speed, short-distance communication in embedded systems and various electronic devices.
Q28) Is SPI good for long distance?
SPI may face signal integrity challenges over long distances due to its simple structure. For longer distances, other communication protocols like RS-485 may be more suitable.
Q29) What is SPI transfer?
SPI transfer refers to the exchange of data between a master device and one or more slave devices using the SPI protocol. It involves the synchronous transmission and reception of data over the SPI bus.
Q30) What are the features of SPI?
Key features of SPI include full-duplex communication, support for multiple slave devices, high-speed data transfer, simplicity in implementation, and versatility across various applications.
Q31) What is SPI isolator?
An SPI isolator is a device that provides electrical isolation between the master and slave devices in an SPI communication system. It helps protect sensitive components and prevent ground loops.
Q32) What is SPI DC PIN?
The SPI DC (Data/Command) pin is not a standard part of the SPI protocol. However, in some applications, it may refer to a pin used to distinguish between data and command signals when interfacing with certain display modules.
Q33) Does SPI need resistors?
Although resistors are not obligatory for fundamental SPI communication, they find utility in tasks such as signal conditioning, impedance matching, or resolving specific issues like signal reflections in long-distance applications.
Q34) Can SPI be half duplex?
Although SPI is inherently a full-duplex protocol, one can configure it to operate in a half-duplex mode by disabling either the master’s transmit capability or the slave’s transmit capability at a given time.
Q35) How much current does SPI use?
The current consumption of an SPI bus depends on factors such as the number of devices connected, their power requirements, and the specific operational conditions. It’s crucial to check the datasheets of the connected devices for accurate information.
Q36) How many bits does SPI send?
The number of bits sent in an SPI communication is determined by the data format specified for the particular application. It can range from 8 to 16 bits or even more, depending on the devices involved.
Q37) What is SPI timing?
SPI timing refers to the synchronization and timing requirements for data transmission and reception in an SPI communication system. It involves parameters such as clock frequency, setup time, hold time, and data transfer rate.
Q38) What is the lowest frequency of SPI?
The lowest frequency of SPI depends on the specific devices connected and their operational requirements. SPI can operate at very low frequencies if needed, making it versatile for various applications.
Q39) What is master mode in SPI?
In SPI, the master mode refers to the operational state where a master device initiates and controls communication with one or more slave devices on the SPI bus.
Q40) Does SPI use timer?
While SPI itself does not require a dedicated timer, microcontrollers or other devices using SPI may employ timers for accurate clock generation, synchronization, or to manage specific timing aspects of SPI communication.
Q41) Is SPI full or half duplex?
SPI operates in full-duplex mode, allowing simultaneous transmission of data in both directions. This capability is achieved by utilizing separate lines for transmitting data from the master to the slave (MOSI) and from the slave to the master (MISO).
Q42) Is SPI full-duplex or half duplex?
SPI is full-duplex, supporting simultaneous data transmission and reception between the master and slave devices.
Q43) What type of flash is SPI?
SPI flash refers to flash memory devices that utilize the SPI protocol for communication. These flash devices are commonly used for storing firmware, configuration data, or other non-volatile information in embedded systems.
Q44) What is the length of SPI cable?
The length of an SPI cable is influenced by factors such as signal integrity requirements, cable quality, and the specific devices connected. Generally, SPI is suitable for short-distance communication within a circuit board or between closely located devices.
Q45) Does SPI need ground?
Yes, SPI requires a common ground reference between the master and slave devices to establish a stable electrical connection and ensure proper signal integrity. A shared ground is essential for accurate data transmission and reception in an SPI system.
Q46) Does start-stop bit support by SPI?
No, SPI (Serial Peripheral Interface) does not use start and stop bits like asynchronous communication protocols such as UART. SPI is synchronous and relies on the master generating a clock signal to initiate and synchronize data transfer. The absence of start and stop bits contributes to the simplicity and efficiency of SPI communication.
Q47) Does pullup register require in SPI?
Pull-up resistors may be necessary for certain SPI configurations, especially in systems where devices share a common bus. The use of pull-up resistors on the MOSI, MISO, and SCLK lines can help maintain signal integrity and prevent floating signals when devices are not actively driving the lines. However, the need for pull-up resistors depends on the specific requirements and characteristics of the SPI bus in a given application.
Q48) Does bus arbitration support by SPI?
Bus arbitration, as commonly understood in the context of multiple devices contending for control of a shared bus, is not a standard feature of SPI. In SPI, the master device controls communication with selected slave devices through the use of the SS/CS (Slave Select/Chip Select) lines. Each slave device is individually selected by activating its SS/CS line, avoiding the need for bus arbitration.
Q49) Does clock stretching support by SPI?
Clock stretching is a feature where a slave device can temporarily hold the clock line low to slow down data transmission, allowing it time to process or respond. SPI does support clock stretching, and its implementation is device-specific. Some SPI devices may have clock stretching capabilities, allowing them to extend the clock low period if necessary for proper communication with the master device. The support for clock stretching depends on the specific SPI device in use.
Q50) Does SPI slave acknowledge the receipt of data?
No, in the standard configuration of the Serial Peripheral Interface (SPI), the slave does not explicitly acknowledge the receipt of data. SPI is a synchronous communication protocol where the master controls the data transfer, and the slave responds to the commands initiated by the master.
In SPI, the master sends data to the slave on the MOSI (Master Out, Slave In) line, and simultaneously, the slave sends data to the master on the MISO (Master In, Slave Out) line. The acknowledgment or confirmation of data reception is implicit in the fact that the slave responds with valid data on the MISO line during the same clock cycle.