CSC270—Circuits & Systems · 2019-04-02 · D. Thiebaut, Computer Science, Smith College Feedback...

mith College

Computer Science

Dominique Thiébaut [email protected]

CSC270—Circuits & Systems

Week 9 — Spring 2019

D. Thiebaut, Computer Science, Smith College

Continue Last Lab

(30 Minutes)

https://xkcd.com/730/


Feedback on HW #5

• Make your program test all interesting starting states. Do NOT modify and restart by hand. While this is fine for a handful of cases, it is better to let the program do all the work, not the programmer!

• The second part asked to change the design. Once the change is made, verify that it will work as you expect using the Python simulator.


Arduino-to-ArduinoCommunication

Arduino-to-ArduinoCommunication


Sources forMaterial Covered

• Chapter 7 of Programming in C for the Arduino by Julien Bayle (https://doc.lagout.org/programmation/C/

C%20Programming%20for%20Arduino%20%5BBayle%202013-05-17%5D.pdf)

• Serial Communication: https://www.arduino.cc/en/Tutorial/MultiSerialMega

• I2C: wire library: https://www.arduino.cc/en/reference/wire


Outline

• Parallel Communication

• Terminology

• Serial Communication

• Handshake

• Arduino Serial

• I2C


Parallel CommunicationSender

STB ACK

D0 D1 D2 D3 D4 D5 D6 D7

GND

Receiver

STB ACK D0 D1 D2 D3 D4 D5 D6 D7

GND


Protocol forParallel Exchange of Data

STB

ACK

DATA


http://theconversation.com/shaking-hands-is-disgusting-heres-what-else-you-can-do-98097

D. Thiebaut, Computer Science, Smith CollegeD. Thiebaut, Computer Science, Smith College

Rule #1: GroundSender and Receiver!


Rule #2: Provide a Path for return current


Example

• Centronics Interface (old)


Features ofParallel Protocol

• When sender and receiver have different speeds?

• Wiring?

• Connectors?


Arduino ParallelProtocol Algorithm



QuestionHow fast could twoArduinos transfer a byte

from one to the other,using this parallel

protocol?

P.S. You know enough to answer in bytes/second (approximately)



Outline

• Parallel Communication

• Terminology

• Serial Communication

• Handshake

• Arduino Serial

• I2C


Terminology• Synchronous vs asynchronous communication

• Synchronous: a clock signal is sent along with the data for the receiver to recognize each data word

• Asynchronous: no clock signal is sent.

• Simplex, half-duplex, and full-duplex

• Simplex: unidirectional only

• half-duplex: bidirectional, but only one dir at a time

• full-duplex: bidirectional, both directions at the same time


QuestionThe parallel protocol

we just saw is…

_________________ &

_________________

Question


Serial Communication


Many Protocols

• RS232 (old, but defines serial comm)

• USART: Universal Synchronous/Asynchronous Receiver/Transmitter (https://www.arduino.cc/en/Tutorial/MultiSerialMega)

• I2C (https://www.arduino.cc/en/Tutorial/MasterWriter)

• SPI (https://www.arduino.cc/en/Reference/SPI)

• USB (https://en.wikipedia.org/wiki/USB)


Bytes Can Be Sent SeriallyEasily

D Q D Q D Q 0

load/shift


74LS165


RS-232• See Serial Port on Wikipedia (https://

en.wikipedia.org/wiki/Serial_port)

• Old. Created in 1960

• Can be implemented with 3 wires (although the standard called for a 25- or 9-pin connector)

TxD

RxD

GND

TxD

RxD

GND


Sending 1 ByteOver RS232

Voltage

time


8-N-1: Most Common

• 8 = number of data bits

• N = No Parity

• 1 = 1 Stop bit

• Typical use: 9600/8N1


Standard Transmission Speeds

110 300600 12002400 48009600 1440019200 2880038400 5600057600 115200


Arduino-to-ArduinoCommunication Using USARTs

• Serial 0: 0(RX), 1(TX) USB to laptop

• Serial 1: 19(RX), 18(TX)

• Serial 2: 16(RX), 17(TX)

• Serial 3: 15(RX), 14(TX)


An Example: Using Serial1

ReceiverLaptop

Sender




https://www.youtube.com/watch?v=5y1Sp-PM0_w&feature=youtu.be



Another Serial Protocol:The I2C Protocol


Features• Serial communication over a bus

• 100KHz standard (100,000 bits/sec). 400KHz, 1MHz, 3.4MHz also possible, but will depend on processor speed.

• 3 wires: clock, data, ground

• 1 controller/many peripherals

• Up to 127 peripherals

• One to one communication ("Master/Slave")

• Automatic error detection (ensure correct byte exchange)


Video 1: I2C

https://www.youtube.com/watch?v=qeJN_80CiMU


Video 2: I2C

https://www.youtube.com/watch?v=6IAkYpmA1DQ


Open-DrainOpen-Collector


Open-DrainOpen-Collector


74LS07


Recap for I2C Communication

1. Get address of device to communicate with on I2C Bus

2. Get addresses of registers in device that contains the bytes (read or write)

3. Write sketch (Use the "Wire" library on Arduino, #include <Wire.h>)

4. In loop() function:

1. Initiate communication. Specify address of device to talk with

2. Write or read to/from device

3. Close communication


I2C Examplehttps://www.arduino.cc/en/Tutorial/MasterReader


Example 1https://www.arduino.cc/en/Tutorial/MasterReader

on Mega 2

560

SDA=Pin 20

SCL=Pin 21






Modern SerialInterface: USB

• Started 1996 (USB 1.0)

• For data and power (5V)

• High Speed (1.5Mbits/s —> 40GBits/s)

• Several Layers of Software

• Exchanges data in packets

• Uses some form of Acknowledge

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CSC270—Circuits & Systems · 2019-04-02 · D. Thiebaut, Computer Science, Smith College Feedback...

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