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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
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 0s and 1s. 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.
tThe 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
LM335 Temperature Sensor
The LM335A works like a Zener diode with a breakdown voltage proportional to absolute
temperature at 10mV/°K. Hook up a resistor from 5V and GND, and the LM335A will output
an analog voltage of 2.98V (298 Kelvin is 25C 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 LM335.
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
D18BS20 Temperature Sensor
Very similar to the LM335, but each has its own unique 64 bit number etched onto it so that
The sensor can be identified. Why might that be useful?