Lec2 Hardware Connections

7/25/2019 Lec2 Hardware Connections

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MICROPROCESSOR BASE

EMBEDDED SYSTEM

DESIGN

Syed Ali Jabir

Lecture

2

Email:

[email protected]
mailto:[email protected]:[email protected]


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PIC18F4520 PIN CONNECTIONS


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Vdd (Vcc)

Two pins

+5V

Some PIC18F family members have lower voltage for Vdd

Reduces noise

Reduces power consumption

Voltage level can be changed setting appropriate bits in

configuration register


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Vss (GND)

Two pins

Typically multiple pins for Vcc and GND help reduce

noise in high frequency systems


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`MCLR

Pin 1 is the Master CLear Reset

It is an input and active-LOW

When low pulse is applied, the microcontroller will

reset and terminate all activities

Also called Power-On Reser (POR)


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`MCLR

Typical connections

Vdd

MCLR

10K

Vdd

MCLR

10K

270Push

Button


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`

OSC1 & OSC2

PIC18F can be operated in 10 different oscillator modes

We can select the mode by setting bits FOSC3:FOSC0, in

configuration register 1H

Mostly a quartz crystal of up to 40MHz is connected to

input pins OSC1 and OSC2


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OSC1 & OSC2

1 LP Low Power Crystal

2 XT Crystal/Resonator

3 HS High Speed Crystal/Resonator

4 HSPLL High Speed Crystal/Resonator with PLL enabled

5 RC External Resistor/Capacitor with FOSC/4 output on RA6

6 RCIO External Resistor/Capacitor with I/O on RA6

7 INTIO1 Internal Oscillator with FOSC/4 output on RA6 and I/O on R

8 INTIO2 Internal Oscillator with I/O on RA6 and RA7

9 EC External Clock with FOSC/4 output

10 ECIO External Clock with I/O on RA6


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OSC1 & OSC2


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`

`

` `

` `

`

`


Ports

A

B

CD

E`


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RECAP

Which pin is used for reset in PIC18F4520 ?

MCLR is active - ?

How many Vdd and Vcc pins are there in PIC18F4520 ?


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Configuration Registers


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CONFIG1H register and Oscillator Clock Source

Located at address 0x300001

Is used for clock oscillator settings


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11XX External RC oscillator, CLKO function

101X External RC oscillator, CLKO function o

1001 Internal oscillator block, CLKO function on RA6, po

1000 Internal oscillator block, port function on RA

0111 External RC oscillator, port function on

0110 HS oscillator, PLL enabled (Clock Frequency =0101 EC oscillator, port function on RA6

0100 EC oscillator, CLKO function on RA

0011 External RC oscillator, CLKO function o

0010 HS oscillator

0001 XT oscillator

0000 LP oscillator


CONFIG1H register and Oscillator Clock Source

FOSC3:FOSC0

Oscillator Selection

bits


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Instruction Cycle Time

In PIC18F microcontrollers, instruction cycle time is based on of the

provided to OSC pins

So if we use 4MHz crystal

4MHz/4 = 1MHz

Inst. cycle time = 1/1MHz = 1us

Compute Instruction cycle time for 10MHz crystal


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CONFIG2L register and reset voltage


Is used for providing stable voltage and clock frequency during reset

An internal power up timer (PWRT) provides a fixed delay during po

which keeps CPU in reset state until power supply stabilizes

Another internal oscillator startup timer (OST) does the same for cry


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CONFIG2L register and reset voltage

Microcontroller can malfunction if power source provided to Vdd pins

Brown Out Reset Voltage (BORV) lets the user set a minimum voltage b

microcontroller goes into reset state

For a high speed crystal of 40MHz, Vdd = 5V and BORV = 4.5V

For low power systems BORV = 1.8V

Once the voltage stabilizes, program continues execution from the sam


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CONFIG2H register and watch dog timer


WATCH DOG TIMER is used to force the microcontroller into the known state o

when the system is hung up or out of control due to execution of incorrect sequ

Problems can happen due to corruption of program memory caused by

Power surge

Electrically noisy environment Inadvertent changes to PC

WDT will force the system into a state of reset/sleep from which it can recover

USES

Prevent a system from going into infinite loop due to software bug

Catch events that cause the system to hang


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CONFIG4L register and background debugger


DEBUG

If PIC18F is connected to an in-circuit debugger (Pickit) RB6 and RB7 pins

cannot be used as general purpose I/O

STVREN

Stack Full/Underflow Reset Enable

LVP

Used for low-voltage in-circuit serial programming (ICSP) via pin RB5


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Setting CONFIG registers in MPLAB C18 compil

#include

#pragma config OSC = HS

#pragma config BORV = 45, PWRT = ON, BOR = ON

#pragma config WDT = OFF

#pragma config DEBUG = OFF, LVP = OFF

void main (void)

{

..

..

.

}


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REFERENCES

PIC18F4520 datasheet

Date post:	13-Apr-2018
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