1. Serial Peripheral interface (SPI) bus

• SPI bus was developed by Motorola.

• Protocol : Synchronous bus

  $ \hspace{1cm}\hspace{1cm} $: Full duplex, Bidirectional bus

• SPI is a 4-wire bus i.e.it uses 4 wires. i.e 4 signals: SCLK for serial clock, MOSI, MISO, and $\overline{SS}$.

• Master in slave out(MISO): This signal carries the data from master to the slave.

• Master out slave in(MOSI): This signal carries the date from the device(slave) to the master.

• Serial clock: This is the synchronising pulse.

• Slave select($\overline{SS}$): It is an active low signal to select slave devices.

• SPI is commonly used for high speed communication between and peripheral devices such as EEPROM, data converters and display drivers.

• Master provides the clock to the slave devices. Master also selects the slave devices by enabling $\overline{SS}$ pin.

• Speeds: SPI provides speed up to 4 Mbps.

• Interfacing diagram

2. RS232

(i) RS232C communication is between DTE (computer) COM port and DCE (modem) port.

(ii) DTE - Data Terminal Device, DCE - Data communication Device

(iii) Protocol : RS232 is a full duplex bus(serial communication).

(iv) Logic level :

Receiver end $\;\implies\;$ -3V to -25V $\;\implies\;$ logic '1'

$\hspace{4cm} $+3V to 25V $\;\implies\;$ logic '0'

Transmitter end $\;\implies$-5V to -15V $\;\implies$ logic '1'

$\hspace{4cm}$+5V to +15V $\;\implies$ logic '0'

(v) Speed : Generally 9600 baud/s.

When transmitting up 0.25 m on cable, the max. baud rate can be 11.5.2 K or 38.4 K baud/s respectively.

(when length of cable increases, speed decreases)

(vi) Cable: untwisted pair cable, 50 feet maximum.

(vii) Connector : RS232 DB-9 connector

• (1) $\overline{DCD}$ - data carrier detect

• (2) RxD - Received data

• (3) TxD - Transmitted data

• (4) $\overline{DTR}$ - Data terminal ready

• (5) GND - Signal Ground

• (6) $\overline{DSR}$ - Data set Ready

• (7) $\overline{RTS}$ - request to send

• (8) $\overline{CTS}$ - Clear to send

• (9) RI - ring indicator

3. RS485

(i) Protocol - RS485 uses half duplex or serial communication protocol.

(ii) Logic level - Electric signal between +12V and -7V

logic '1' is +ve (0-12V)

logic '0' is -ve (-7 to 0V)

(iii) Speed - 35Mbps upto 10 meter

100Kbps upto 1.2 km

(iv) Cable length - 4000 feet maximum

(v) Network - 32 driver and 32 receivers

(vi) Signal

(+6V - permissible range)

4 Comparison between RS485 and RS232

RS232

Mode of operation - Single ended

Total no. of drivers - 1 Driver

Total no. of receivers - 1 receiver

Max.cable length - 50 feet

Speed - 115.3 K baud/s at 0.25 m

Logic levels 1) logic 0 $\to$ +3V to 25V

$\hspace{2.5cm}$2) logic 1 $\to$ -3V to -25V

Input resistance of receiver - 3k$\Omega$ to 7k$\Omega$

Slew rate(max) - 30V/$\mu$s

RS485

Mode of operation - Differential

Total no. of drivers - 32 drivers

Total no. of receivers - 32 receivers

Max.cable length - 4000 feet

Speed - 50Mbps at 50 feet

Logic levels 1) logic 0 $\to$ -7V to 0V

$\hspace{2.5cm}$2) logic 1 $\to$ 0V to 12V

Input resistance of receiver - $\ge$12k$\Omega$

Slew rate(max) - N/A

5. $1^2$C

(i) $1^2$C is a serial bus for interconnecting ICs

(ii) $1^2$C uses bidirectional serial communication protocol for communicating between Integrated Circuits(ICs).

(Assume there are n no. of device ckts in a process,one IC for each particular function. To connect theses ICs mutually with each other, common sync bus is used called $1^2$C.)

(iii) $1^2$C has 2 lines to carry it's signals,SCL-Serial clock,SDA-Serial Data.

(iv) Each device has an address through which data transfer takes place. Master can address up to 127 slaves at an instance. There can be more than 1 master as well. However, at any instance, there can be only one master which is one that initiates data transfer on SDA(serial data) and which transmits the SCL(serial clock) pulses.

(v) Interfacing Diagram

6. Parallel Data transfer and serial data transfer

Parallel data transfer

(i) Multiple data bits are transferred at a time.

(ii) Multiple lines are required to be connected between the transmitter and the receiver.

(iii) Data transfer speed is high.

(iv) Small distance communication only.

Serial data transfer

(i) One bit of data.

(ii) Maximum of two lines are to be connected between the transmitter and the receiver.

(iii) Data transfer speed is low.

(iv) Long distance communication.

7. USB

(i) Protocol : Sync half duplex, serial data communication with differential data.

(ii) Logic level

(iii) Speed

(iv) Wire/cable : 4 wire cable[Unshielded twisted pair]

(v) Cable length : Max 16 feet/segment

$\hspace{2cm}$Max. 6 cascaded segment in network

$\hspace{2cm}$Max host to device $\implies$ 96 feet.

(vi) Connector : Type A(upstream) sys side

$\hspace{2.5cm}$ : Type B(downstream) server

(vii) Network : Tree network

$\hspace{3cm}$ 7 bit identification field

$\hspace{3cm}$ $\therefore 2^7 = $ 128 devices.

$\hspace{3cm}$0 - 127 Ids

$\hspace{3cm}$0 $\implies$ host $\implies$127 Ids for 127 devices.

(viii) Signal

8. Bluetooth

(i) Protocol : Sync, full duplex serial data communication(802.15.1 protocol), low cost, low power short range wireless technology for data and voice communication.

(ii) Operates at 2.4 GHz of Radio frequency spectrum and used Frequency Hopping spread spectrum.

(iii) Data rate is 1Mbps.

(iv) BT devices - BT wireless radio for transmission and reception of data, 48 bit certification no.

(v) BT supports point to point and point to multi-point communication.

(vi) BT supports range upto 10m low power and upto 100 high power.

9. Zigbee

(i) IEEE standard 802.15.4 protocol.

(ii) Physical radio layer : 24 GHz band carrier frequency with DSSS(direct signal spread spectrum)

(iii) It supports range upto 70m. Data transfer rate is 250Kbps and supports 16 channels.

(iv) Zigbee network :

• Zigbee network is self organizing, detects nearby zigbee devices and establish communication

• supports peer to peer and mesh networks. Each node at network functions as requesting as well as responding device.

• means each network functions as mesh.

• node is connected to another node directly or through mutually interconnected nodes.

• data transfer = 2 devices peer to peer

  $\hspace{2.5cm}$= 1 device and multiple devices - mesh network

(v) Zigbee protocol supports large number of sensors, lighting devices, air conditioning and other devices for home and office automation.

(vi) Zigbee network

Zigbee router : transfer packets from neighbour source to nearby node.

Coordinator : connects one zigbee network with another connects WLAN or cellular network.

End devices : transceivers of data.