Use Timer0, Timer1 and Timer2. Use interrupts, declare new procedure...

If you have read previous examples, you have probably noticed a disadvantage of using time delays. In all those cases, the microcontroller is ‘captive’ and does nothing. It simply waits for some time to pass. Such waste of time is often an unacceptable luxury and some other method should be employed here. Do you remember the story about timers? Interrupts? This example makes connection between them in a practical way. The schematic is still the same and challenge as well. It is necessary to provide a time delay long enough to notice changes on a port. Timer TMR0 with assigned prescaler is used for this purpose. An interrupt is generated on every timer register overflow and every interrupt routine increments the cnt variable by 1. When it reaches 50, the PORTB is incremented by 1. The whole procedure is performed ‘behind the scenes’, which enables the microcontroller to do something else.

' Header******************************************************
program example_4a ' Start of program
dim cnt as byte ' Define variable cnt as byte

sub procedure interrupt ' This subprocedure determines what should
 ' be done when an interrupt is generated
cnt = cnt + 1 ' Interrupt causes cnt to be incremented by 1
TMR0 = 96 ' Timer TMR0 is returned its initial value
INTCON = 0x20 ' Bit T0IE is set, bit T0IF is cleared
end sub ' End of interrupt routine

main: ' Start of program
OPTION_REG = 0x84 ' Prescaler is assigned to timer TMR0
ANSEL = 0 ' All I/O pins are configured as digital
ANSELH = 0
TRISB = 0 ' All PORTB pins are configured as outputs
PORTB = 0x0 ' Reset PORTB
TMR0 = 96 ' Timer T0 counts from 96 to 255
INTCON = 0xA0 ' Enable interrupt TMR0
cnt = 0 ' Variable cnt is assigned a 0

while 1 ' Endless loop
if cnt = 50 then ' Increment PORTB after 50 interrupts
PORTB = PORTB + 1 ' Increment number on PORTB by 1
cnt = 0 ' Reset variable cnt
end if
wend

end. ' End of program

An interrupt is generated on every timer register TMR0 overflow.

'Header******************************************************
program example_4b ' Program name
dim cnt as byte ' Define variable cnt

sub procedure interrupt ' Define interrupt subprocedure
cnt = cnt+1 ' Interrupt causes cnt to be incremented by 1
PIR1.TMR1IF = 0 ' Reset bit TMR1IF
TMR1H = 0x80 ' TMR1H and TMR1L timer registers are returned
TMR1L = 0x00 ' their initial values
end sub ' End of interrupt routine

main: ' Start of program
ANSEL = 0 ' All I/O pins are configured as digital
ANSELH = 0
PORTB = 0xF0 ' Initial value of PORTB bits
TRISB = 0 ' PORTB pins are configured as outputs
T1CON = 1 ' Set timer TMR1
PIR1.TMR1IF = 0 ' Reset bit TMR1IF
TMR1H = 0x80 ' Set initial value for timer TMR1
TMR1L = 0x00
PIE1.TMR1IE = 1 ' Enable interrupt on overflow
cnt = 0 ' Reset variable cnt
INTCON = 0xC0 ' Enable interrupt (bits GIE and PEIE)

while 1 ' Endless loop
if cnt = 76 then ' Change PORTB state after 76 interrupts
PORTB = not PORTB ' Number in PORTB is inverted
cnt = 0 ' Reset variable cnt
end if
wend

end. ' End of program

In this case, an interrupt is enabled after the timer register TMR1 (TMR1H and TMR1L) overflow occurs. The combination of bits changing on PORTB is different from that in the previous example.

'Header******************************************************
program example_4c ' Program name
dim cnt as byte ' Define variable cnt as byte

sub procedure Replace ' Define procedure Replace
PORTB = not PORTB ' Define new procedure ‘Replace’
end sub ' Procedure inverts port state

sub procedure interrupt ' Define interrupt subprocedure
if PIR1.TMR2IF then ' If bit TMR2IF = 1,
cnt = cnt +1 ' Increment variable cnt by 1
PIR1.TMR2IF = 0 ' Reset bit and
TMR2 = 0 ' reset register TMR2
end if
end sub ' End of interrupt routine

main: ' Start of program
cnt = 0 ' Reset variable cnt
ANSEL = 0 ' All I/O pins are configured as digital
ANSELH = 0
PORTB = %10101010 ' Logic state on PORTB pins
TRISB = 0 ' All PORTB pins are configured as outputs
T2CON = 0xFF ' Set timer T2
TMR2 = 0 ' Initial value of timer register TMR2
PIE1.TMR2IE = 1 ' Enable interrupt
INTCON = 0xC0 ' Set bits GIE and PEIE

while 1 ' Endless loop
 if cnt > 30 then ' Change PORTB after more than 30 interrupts
 Replace ' Function Replace inverts the PORTB state
 cnt = 0 ' Reset variable cnt
 end if
wend

end. ' End of program

This time, an interrupt is generated after timer register TMR2 overflow occurs. The Replace procedure, which normally doesn’t belong to mikroBasic, is used in this example to invert port pins state.