SPI Serial Peripheral Interface SPI Serial Peripheral Interface

SPI Serial Peripheral Interface

SPI Serial Peripheral Interface is communication between two devices, one bit at a time sequential one bit at time over a computer bus ( a subsystem that transfers data Between components inside of a computer) or a communication channel (wire or wave transmission). Serial Peripheral Interface (SPI) is a synchronous serial data protocol used by microcontrollers for communicating with one or more peripheral devices quickly over short distances. It can also be used for communication between two microcontrollers.

Communication Channel

Computer Bus

SPI Serial Peripheral Interface is a synchronous data link that operates in full duplex mode which means that communication can occur in both directions simultaneously. cell phones and two way radios are full duplex devices. Devices operate in a master/ slave mode where the master initiates and directs the communication of data. Some times SPI is called a 4 -wire serial bus.

SPI

SPI has 4 logic signals. A logic signal is the finite number of states a signal can have. The logic signal we are most familiar with is binary 0 s and 1 s. Logic levels are represented by a difference in voltage. SCLK MOSI MISO SS

SCLK Serial Clock is output from the master. The serial clock sets the frequency of communication To begin a communication, the bus master first configures the clock, using a frequency less than or equal to the maximum frequency the slave device supports. Such frequencies are commonly in the range of 1– 100 MHz The clock pulses which synchronize data transmission generated by the master

SS Slave Select is active when the logic signal is low. If there is only one slave device then the SS pin maybe fixed at logic low. If there are multiple slave devices then the signal is low signifying which of the devices is “conversing” with the master. t. The pin on each device that the master can use to enable and disable specific devices. The master then transmits the appropriate chip select bit for the desired chip to a logic 0. A logic 0 is transmitted because the chip select line is active low, meaning its off state is a logic 1; on is asserted with a logic 0.

MOSI Master Output, Slave Input. Output from the Master. Serial data in. The Master line for sending data to the peripherals, During each SPI clock cycle, a full duplex data transmission occurs: the master sends a bit on the MOSI line; the slave reads it from that same line

MISO Master Input, Slave Output. Input from the Master. Serial data out. The Slave line for sending data to the master. The slave sends a bit on the MISO line; the master reads it from that same line. Transmissions may involve any number of clock cycles. When there is no more data to be transmitted, the master stops toggling its clock. Normally, it then deselects the slave.

Multiple Slave Configuration When a device's Slave Select pin is low, it communicates with the master. When it's high, it ignores the master. This allows you to have multiple SPI devices sharing the same MISO, MOSI, and CLK lines.

What components or devices have we used that use SPI? There are three so far.

Sensors: temperature, pressure, ADC, touchscreens, video game controllers Control devices: audio codecs, digital potentiometers, DAC Camera lenses: Canon EF lens mount Communications: Ethernet, USB, USART, CAN, IEEE 802. 15. 4, IEEE 802. 11, handheld video games Memory: flash and EEPROM Real-time clocks LCD displays

Sensors: temperature, pressure, ADC, touchscreens, video game controllers Control devices: audio codecs, digital potentiometers, DAC Camera lenses: Canon EF lens mount Communications: Ethernet, USB, USART, CAN, IEEE 802. 15. 4, IEEE 802. 11, handheld video games Memory: flash and EEPROM Real-time clocks LCD displays

LM 335 Temperature Sensor The LM 335 A works like a Zener diode with a breakdown voltage proportional to absolute temperature at 10 m. V/°K. Hook up a resistor from 5 V and GND, and the LM 335 A will output an analog voltage of 2. 98 V (298 Kelvin is 25 C or room temperature). The sensor can operate continuously from − 40°C to 100°C. Calibration of the sensor requires a pot connected across the sensor, with the wiper of the potentiometer connected to the adjustment pin of the LM 335. A Zenner diode allows current to flow in the forward direction in the same manner as an ideal diode, but will also permit it to flow in the reverse direction when the voltage is above a certain value

D 18 BS 20 Temperature Sensor Very similar to the LM 335, but each has its own unique 64 bit number etched onto it so that The sensor can be identified. Why might that be useful?