This document discusses various communication buses and protocols used for embedded networking. It describes serial communication protocols like RS-232, RS-485, CAN, I2C, SPI and parallel communication interfaces like parallel port, PCI, and SCSI. It provides details on the specifications, features, and applications of each protocol.

1. EMBEDDED NETWORKING
A.ARULKUMAR
Asst. Professor
Dept. of Mechatronics Engineering
Kamaraj College of Engg & Tech.

2. Devices and Communication Buses for
Embedded Networking
• I/O ports – Serial and Parallel
• Interfacing of devices through ports
• Timer
• Real Time Clock
• Networked Embedded Systems
• Serial / Parallel Bus communication protocols
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3. Hardware units - I/O buses
• Serial Bus examples:
– RS232 (20kBaud)
– CAN (33 kbps)
• Controller Area Network
– Fault tolerant CAN (110
kbps)
– SM I2C (100kbps)
• System Management
– SPI (100 kbps)
• Serial Peripheral Interface
– MicroWire (300 kbps)
– FireWire/IEEE 1394 (400
Mbps, 72m)
– High Speed USB 2.0 (480
Mbps, 25m)
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• Parallel bus examples
• SCSI parallel (40 Mbps),
• Small computer System interface
• Used for interfacing Hard drive,
CDROM, within the system
• Fast SCSI (8M to 80 Mbps) & Ultra
SCSI-3 (8M to 160 Mbps)
• For interfacing more devices to a
processor at higher burst transfer
rates
• PCI
• PCI-X

4. I/O Port
• To exchange bytes between the processor and external devices
using processor instructions
• Connected using address decoder and system bus
• Addresses of the port-registers used for
– programming the port functions or modes
– reading port status
– writing or reading bytes
• Serial port:
– sync / async,
– input / output / IO
• Parallel port:
– single bit / multibit,
– input / output
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5. Serial Communication modes
• Half duplex
– Between Modem and telephone line
• Full duplex
– Between Modem and Processor

6. Serial Communication Protocols
• A protocol is a standard adopted which tells the way in
which the bits of a frame must be sent from a device (or
controller or port or processor) to another device or system
• Protocol identification:
– Type: Sync / Async
– Frame length (variable / fixed)
– Frame contents (Header, address, data, etc.)
– Error control, flow control procedures
• Syncronized communication protocols
– I2C
• Async communication protocols
– RS232

7. Synchronous serial I/O
• The sender (Master) sends SCLK to the receiver (Slave)
• SCLK can be in the same data line or separate line
• Synchronous serial I/O is used for:
– inter-processor transfers
– streaming data,
– multiprocessor communication,
– writing to CD or hard disk,
– network device output
– serial I/O bus output
– writing to flash memory
• No handshaking. Fixed Clock for synchronized
communication
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8. Serial communication –
Synchronization methods
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10. Asynchronous Serial I/O
• Does not use SCLK but uses handshaking
signals for exchanging data
• Each received byte is not in synchronization.
• Bytes are separated by variable intervals or
phase differences
• E.g. Inputs from Keyboard, mouse, modem
through UART using UART standard format
• Async. Serial ports: E.g. COM1 and COM2
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12. RS232
• For asynchronous communication between DTE and DCE
(E.g. Modem and UART)
• uses UART standard format for TxD and RxD lines
– logic 1 (Receiver) – 3 V to – 25 V
– logic 0 (Receiver) + 3 V to + 25 V
– logic 1 (Transmitter) – 5 V to – 15 V
– logic 0 (Transmitter) + 5 V to + 15 V
• opposite to that of TTL logic
• wider noise margin to enable long distance communication
• Handshaking signals
– RI, DCD, DSR, DTR, RTS, CTS, DTR

14. RS232 interface
• Question: What is the difference between Bit rate and Baud rate?
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15. RS422
• Purpose: To extend RS232
• Point to Point, Multi-drop (RS485 is multi-point as it
can have more than 1 driver)
• Max devices 10 (1 driver and 10 receivers)
• Distance 1500m
• Differential mode signal
• Speed 100 kbps to 10Mbps
• Voltage levels: -6 to +6V
• Mark (1) : Negative voltage
• Space (0) : Positive voltage

17. RS485
• Used in Industrial control systems for proprietary automation protocols
• Differential signal is used. Hence EMI is suppressed. Used in PLCs
• Voltage level: RS485 driver provides a differential voltage of 1.5V across 54
Ohm load
• Long distance serial communication (1200m) in electrically noisy
environments
• Multiple receivers can be connected in linear bus topology with multi-drop
configuration
• Termination resistors (120 Ohms for twisted pair) are required
• Speed 35 Mbps (10m) 100 kbps (1200m)
• Rule: speed x length < 108
• Master-slave arrangement: master initiates communication
• Full duplex possible with 4 wires
• Can interoperate with RS422
• No specific connector or pinout.

20. • Asnchronous start-stop method of RS485
communication
• Uses two pins non-inverting pin and inverting
pin

21. Serial Peripheral Interface (SPI)
• Hardware / Firmware communication protocol
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22. Synchronised Serial SPI bus connection
Typical SPI Bus Daisychained SPI bus
(three independent slaves) (three cooperative slaves)
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23. SPI features
• Full-duplex Synchronous communication.
• SCLK, MOSI and MISO signals for serial clock
from master, output from master and input to
master, respectively.
• Device selection as master or slave can be
done by a signal to hardware input SS (Slave
select when 0)

25. I2C bus
• Inter-Integrated Circuit Bus
• Synchronous Serial Bus
• Interconnecting devices & Circuits within the system
• E.g. Flash memory, touch screen, sensor Ics,
• Master and Slave concept
• Master controls the clock and generates START and STOP signals.
• Slaves simply listen to the bus and act on controls and data that they are
sent.
• The master can send data to a slave or receive data from a slave - slaves do
not transfer data between themselves.
• Multi master operation involves arbitration of the bus (where a master has
to fight to get control of the bus) and clock synchronization (each may a use
a different clock e.g. because of separate crystal clocks for each micro).
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27. I2C features
• Three standards
– Industrial 100 kbps I2C
– 100 kbps SM I2C
– 400 kbps I2C
• Each device has 7-bit address
• Master can address 127 slaves
• Master has a bus controller or Microcontroller with I2C bus
interface. Each slave can also optionally have I2C bus
controller and processing element.
• A number of masters can be connected on the bus. But, at
a time, there is only one master which initiates a data
transfer on SDA (serial data) line and which transmits the
SCL (serial clock) pulses.

28. I2C Bits
• START (1) similar to UART
• Address (7) defines the slave address, which is being sent the data frame (of
many bytes) by the master
• R/W (1) defines whether read or write is in progress
• Ack (1) defines whether the present data is an acknowledgment (from slave)
• Data (8) I2C device data byte
• NACK (1) from the receiver. If active then ack is not needed from the slave
• STOP (1) Similar to UART

29. CAN bus
• Developed by Bosch for automotive industry
• Replaces complex wiring harness with simple two-wire bus
• In USB, large blocks of data transferred point-to-point
• In CAN, many short data broadcast throughout the network.
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30. CAN Bus - Features
• Network of embedded systems in an automobile
• Interconnects to a CAN controller between line and
host at the node. Connects the physical and data link
layers at the host node.
• The CAN controller has
– BIU consisting of buffer and driver
– Protocol controller
– Status-cum control registers
– Receiver-buffer
– Message objects.
• The above units connect the host node through the
host interface circuit

32. • Three standards
– 33 kbps CAN,
– 110 kbps Fault Tolerant CAN,
– 1 Mbps High Speed CAN
• CAN protocol
– Carrier Sense Multiple Access with Arbitration on Message Priority basis
• Each distributed node uses
– Twisted Pair Connection up to 40 m for bi-directional data
– Line, which pulls to Logic 1 through a resistor between the line and + 4.5V to
+12V
– Line Idle state Logic 1 (Recessive state)
– a buffer gate between an input pin and the CAN line
• Device Detects Input Presence at the CAN line, pulled down to dominant
or active state (0V) by a sender. The sender device uses a current driver
between the output pin and CAN line to pull down to active state.

33. • Arbitration concept using Remote Transmission Request (RTR)
– RTR=1: Pkt has data for the destn device
– RTR=0: Pkt has a request for data from destination device

34. USB
• Serial transmission and reception between host and serial devices such as:
– flash memory cards, pen-like memory devices, digital camera, printer, mouse-
device, PocketPC, video games, Scanner
• Four types of data transfer:
– Controlled data transfer
– Bulk data transfer
– Interrupt driven data transfer
– Iso-synchronous transfer
• Maximum 127 devices can be connected to host
• Three standards:
– USB 1.1 (a low speed 1.5 Mbps 3m channel along with a high speed 12 Mbps
25 meter channel)
– USB 2.0 (high speed 480 Mbps 25m channel)
– Wireless USB (high speed 480 Mbps 3m)

36. USB & Firewire
• Firewire 400 (400 Mbps)
• USB 2.0 (480 Mbps)
• Firewire 800 (800 Mbps)
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37. Microwire
• Older than SPI
• Faster than I2C
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38. UART
• Any serial device can be connected to the computer through UART
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40. Parallel Port
• Single bit input and output
– Not generally used
• Multibit input
– ADC
– Encoder
• Multibit output
– Printer
– LCD / LED display
• Multibit I/O
– 8255 PPI
– Touchscreen

42. Handshaking signals at the Port
• STROBE
• PORT READY
• BUFFER-FULL
• ACKNOWLEDGE
• INTERRUPT REQUEST

43. Handshaking Procedure for Parallel
Communication
• For input at a port
– Device makes a request to system I/O port – STROBE
– Port sends ack - PORT READY
– Port receives data in receiving buffer
– Port sends INTERRUPT REQUEST to processor indicating receiving-
buffer is full (available for next read)
– Issues INT to processor to enable ISR
• For output at a port
– Processor writes data into transmitting buffer
– Port sends BUFFER FULL to device to inform that buffer is full.
– Device reads message and sends ACKNOWLEDGE
– Port sends INTERRUPT REQUEST to Processor indicating transmitting-
buffer is empty (available for next write)

44. 8255 Programmable Peripheral
Interface
• Four addresses for the PPI port, three for the
ports and one for the control word.
• Three 8-bit ports− port A, B and C.
• Port C programmable to function in bit set
reset mode. Each bit of port C can be set to 1
or reset to 0 by an appropriate control word.
• Alternatively, the ports can be grouped as
Group A (Port A and Port C upper four bits) or
Group B (Port B and Port C lower four bits).

45. Parallel – ISA Bus
• 16-bit and 8-bit ISA slots

46. Parallel communication - PCI
• Peripheral Component Interconnect
• 32 pin interface for connecting additional hardware to a system
• 33 MHz speed
• E.g. Add-on boards, Processor / memory systems
• Not generally used in Embedded systems
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47. Parallel communication – PCI X
• Peripheral component interconnect Extended
• 64 bit operation
• 66 / 100 / 133 MHz speed
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48. Parallel communication - SCSI
• Small Computer System Interface
• Parallel interface standard for connecting peripherals such as
printers, hard disk, CD ROM drive, etc.
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49. THANK YOU