Notes

Basics

There are simpler integrated circuits that have only one function(read a sensor/ control a digital potentiometer/oscillator) to drive a PWM circuit. These ICs have no clock crystal of their own. To communicate with these ICs, use synchronous serial communication.

<aside> ❓ What's the meaning of clock crystal?🤔Is it literal or a fixed definition?

</aside>

2 common forms of synchronous serial:

• SPI - Serial Peripheral Interface
• I2C - Inter-Integrated Circuit(sometimes also called TWI - Two-Wire Interface)

Synchronous serial devices communicate by shifting bits of data along their communication lines. Data moved down the line one bit every time the clock pulses. All the devices in a synchronous serial chain share the same data and clock lines.

Serial Peripheral Interface

A typical SPI bus configuration.

• SDI - Serial Data In (the controller sends data to the peripheral devices.)
• SDO - Serial Data Out (the peripheral devices send data to the controller.)
• **SCLK - Clock (**the controller sends a regular clock signal to the peripheral devices.)
• CS - Chip Select (the controller uses to signal the peripheral devices when to listen to incoming data and when to ignore it.)
• COPI - Controller Out, Peripheral In
• CIPO - Controller In, Peripheral Out

the controller device communicates with one peripheral >> sets the device’s CS pin low

If a peripheral device’s CS pin is high, it will not respond to any commands sent on the data line.

• the rising edge of the clock

  The peripheral listens to the microcontroller’s SDO line every time the clock changes from low to high

• the falling edge of the clock

  If it is instructed to send any data back, it will send data back to the controller when the clock signal changes from high to low

Arduino Uno's SPI pins(same for Nano 33 IoT) | SPI library reference page

• pin 11 - SDO
• pin 12 - SDI
• pin 13 - Clock (SCK)