Examples for Subsystems Within Micro Controller

832019 Examples for Subsystems Within Micro Controller

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Examples for subsystems within microcontroller

Introduction

61 Writing to and reading from EEPROM

62 Processing interrupt caused by changes on pins RB4-RB763 Processing interrupt caused by change on pin RB0

64 Processing interrupt caused by overflow on timer TMR065 Processing interrupt caused by overflow on TMR0 connected to external input (TOCKI)

Introduction

Every microcontroller comprises a number of subsystems allowing for flexibility and wide range of applications These include internal EEPROM memory AD converters serial or other form of

communication timers interrupts etc Two most commonly utilized elements are interrupts andtimers One of these or several in combination can create a basis for useful and practical programs

61 Writing to and reading from EEPROM

Program eepromasm uses EEPROM memory for storing certain microcontroller parameters

Transfer of data between RAM and EEPROM has two steps - calling macros eewrite and eeread Macro eewrite writes certain variable to a given address while eeread reads the given address of

EEPROM and stores the value to a variable

Macro eewrite writes the address to EEADR register and the variable to EEDATA register It thencalls the subprogram which executes the standard procedure for initialization of writing data

(setting WREN bit in EECON1 register and writing control bytes 0x55 and 0xAA to EECON2)



For data to be actually stored in EEPROM 10ms delay is necessary This is achieved by usingmacro pausems In case that this pause is unacceptable for any reason problem can be solved by

using an interrupt for signaling that data is written to EEPROM

eewrite macro addr var

addr Destination address With PIC16F84 there are 68 bytes

of EEPROM for a total address range of 0x00 - 0x44

var Name of the variable to be stored to EPROM

eeread macro addr var



var Name of the variable into which data read from EPROM will be stored

Example Variable volume which is set via buttons RA0 and RA1 will be stored to the address 0 of

EEPROM After reboot when the program is started it first loads the last known value of variablevolume from EEPROM



62 Processing interrupt caused by changes on pins RB4-RB7

Program intportbasm illustrates how interrupt can be employed for indicating changes on pinsRB4-RB7 Upon pushing any of the buttons program enters the interrupt routine and determines

which pin caused an interrupt This program could be utilized in systems with battery powersupply where power consumption plays an important role It is useful to set microcontroller to low

consumption mode with a sleep instruction Microcontroller is practically on stand-by savingenergy until the occurrence of interrupt



Example of processing interrupt caused by changes on pins RB4-RB7



63 Processing interrupt caused by change on pin RB0

Example intrb0asm demonstrates use of interrupt RB0INT Upon falling edge of the impulsecoming to RB0INT pin program jumps to subprogram for processing interrupt This routine then

performs a certain operation in our case it blinks the LED diode on PORTB 7



Example of processing interrupt caused by changes on pin RB0

64 Processing interrupt caused by overflow on timer TMR0

Program inttmr0asm illustrates how interrupt TMR0 can be employed for generating specific

periods of time Diodes on port B are switched on and off alternately every second Interrupt is

generated every 5088ms in interrupt routine variable cnt is incremented to the cap of 196 thus



generating approx 1 second pause (5088ms196 is actually 099248s) Pay attention toinitialization of OPTION register which enables this mode of work for timer TMR0

Example of processing interrupt caused by overflow on timer TMR0





65 Processing interrupt caused by overflow on TMR0 connected

to external input (TOCKI)

Counter TMR0 increments upon signal change on pin RA4TOCKI Prescaler is set to 4 meaning

that TMR0 will be incremented on every fourth impulse Pay attention to initialization of OPTIONregister which enables this mode of work for timer TMR0 (this mode is common for devices such ascounters)

Example of processing interrupt caused by overflow on timer TMR0 connected to TOCKI





For data to be actually stored in EEPROM 10ms delay is necessary This is achieved by usingmacro pausems In case that this pause is unacceptable for any reason problem can be solved by

using an interrupt for signaling that data is written to EEPROM

eewrite macro addr var



var Name of the variable to be stored to EPROM

eeread macro addr var



var Name of the variable into which data read from EPROM will be stored

Example Variable volume which is set via buttons RA0 and RA1 will be stored to the address 0 of

EEPROM After reboot when the program is started it first loads the last known value of variablevolume from EEPROM





























































































































































































Examples for Subsystems Within Micro Controller

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