Pic Project

8/14/2019 Pic Project

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REAL-TIME DATA ACQUISITION

FROM TEMPERATURE AND

LIGHT SENSORS

Robin Jacob


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Serial Peripheral Interface (SPI)

SPI is a serial bus standard established by

Motorola and supported in silicon products from

various manufacturers. SPI interfaces are available on popular

communication processors such as the MPC8260

and microcontrollers such as the M68HC11.

It is a synchronous serial data link that operates infull duplex (signals carrying data go in both

directions simultaneously).


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SPI

Devices communicate using a master/slaverelationship, in which the master initiates the dataframe.

When the master generates a clock and selects aslave device, data may be transferred in either or

both directions simultaneously.

In fact, as far as SPI is concerned, data are alwaystransferred in both directions.

It is up to the master and slave devices to knowwhether a received byte is meaningful or not.


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SPI

A device must discard the received byte in a

"transmit only" frame or generate a dummy

byte for a "receive only" frame.

Single master, single slave SPI implementation


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SPI

SPI specifies four signals: clock (SCLK); master

data output, slave data input (MOSI); master data

input, slave data output (MISO); and slave select(SS).

SCLK is generated by the master and input to all

slaves. MOSI carries data from master to slave.

MISO carries data from slave back to master.

A slave device is selected when the master asserts

its SS signal.


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SPI

If multiple slave devices exist, the mastergenerates a separate slave select signal for eachslave.

The master generates slave select signals usinggeneral-purpose discrete input/output pins or otherlogic.

This consists of old-fashioned bit banging and canbe pretty sensitive. You have to time it relative tothe other signals and ensure, for example, that youdon't toggle a select line in the middle of a frame.


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SPI

Single master, multiple slave SPI implementation


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SPI

SPI doesn't describe a specific way to implement

multi-master systems, some SPI devices support

additional signals that make such implementationspossible. However, it's complicated and usually

unnecessary, so it's not often done.

A pair of parameters called clock polarity (CPOL)

and clock phase (CPHA) determine the edges ofthe clock signal on which the data are driven and

sampled.


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SPI

Each of the two parameters has two possiblestates, which allows for four possiblecombinations, all of which are incompatible withone another.

A master/slave pair must use the same parameterpair values to communicate.

If multiple slaves are used that are fixed indifferent configurations, the master will have toreconfigure itself each time it needs tocommunicate with a different slave.


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Real-Time Clock (RTC)

Block Diagram of DS1302 RTC


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RTC


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RTC

Registers of DS1302


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RTC

Registers of DS1302


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Temperature Sensor (TS)

Block Diagram of TMP124


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TS

Timing Diagram of TMP124


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TS

Timing Diagram of TMP124


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Light Dependent Resistor (LDR)

Connection Diagram of a LDR


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System Design

Block Diagram of the Complete System


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System Design

The Controller has to read the ADC and the

TS at a fixed pattern say per sec or per

minute. The current time has to be read from the

RTC and to be checked whether there is a

change in the sec/min, if so the ADC andTS has to be read.


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LCD Output

Display Pattern on the LCD


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Peripheral Board

Board outline of the Peripheral Board


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Thank you

Pic Project

Documents

Transcript of Pic Project