sub procedure WordToStr2(dim number as word )       ' This procedure splits number into digits.
dim pp,                             ' It is assumed that the number is not greater
     qq,                             '           than 9999.
     rr,
     sss as word
   sss = (number div 1000) 'sss = 4
   M0  = LED_Mask(sss)
   sss = sss*1000  'sss = 4000

   rr  = (number - sss) div 100   'rr = (4321-4000) mod 100 =3
   M1  = LED_Mask(rr)
   rr  = sss+rr*100   'rr = 4000+300

   qq  = (number -rr) div 10   'qq = 4321 -4300...  = 21 div 10 =2
   M2  = LED_Mask(qq)
   qq  = rr+qq*10 'qq = 4300+20= 4320

   pp  = number -qq 'pp = 4321 - 4320 = 1
   M3  = LED_Mask(pp)
end sub

dim Counter as word
dim BackupC as word
dim i as word
dim M0 as byte
dim M1 as byte
dim M2 as byte
dim M3 as byte
dim T1Count as byte

sub procedure Interrupt
INTCON= $00 ' DISABLE INTERRUPTS
T1Count = T1Count+1
if T1Count = 2 then
T1COUNT = 0
TMR1H = 23
TMR1L = 184
counter = counter + 1
if counter = 10000 then
counter = 0
end if
end if
PIR1.TMR1IE = 0
PIR1.RCIF = 0
PIR1.TXIF = 0
INTCON= %11000000 ' ENABLE INTERRUPTS
end sub

sub function LED_Mask(dim number as byte) as byte ' This function returns led mask for common cathode display.
select case number ' In case 'number' is not in [0..9],
case 0 result = $3F ' mask '0' ' the function will return unknown value
case 1 result = $06 ' mask '1'
case 2 result = $5B ' mask '2'
case 3 result = $4F ' mask '3'
case 4 result = $66 ' mask '4'
case 5 result = $6D ' mask '5'
case 6 result = $7D ' mask '6'
case 7 result = $07 ' mask '7'
case 8 result = $7F ' mask '8'
case 9 result = $6F ' mask '9'
End Select
end sub

sub procedure WordToStr1(dim number as word) ' This procedure splits number into digits.
dim pp as word ' It is assumed that the number is not greater
dim qq as word ' than 9999.
dim rr as word
dim sss as word

'number = 4321
sss = (number div 1000) 'sss = 4
M0 = LED_Mask(sss)
sss = sss*1000 'sss = 4000

rr = (number - sss) div 100 'rr = (4321-4000) mod 100 =3
M1 = LED_Mask(rr)
rr = sss+rr*100 'rr = 4000+300

qq = (number -rr) div 10 'qq = 4321 -4300... = 21 div 10 =2
M2 = LED_Mask(qq)
qq = rr+qq*10 'qq = 4300+20= 4320

pp = number -qq 'pp = 4321 - 4320 = 1
M3 = LED_Mask(pp)
end sub

main:
WordToStr1(20)
INTCON = $00 ' DISABLE INTERRUPTS
TRISB = $00 ' PORTB: ALL OUTPUTS
TRISA = $00 ' PORTA: ALL OUTPUTS
T1COUNT = 0

PIE1.RCIE = 0 ' disable usart interrupts
PIE1.TXIE = 0
PIE1.TMR1IE = 1 ' enable interrupt on timer1 overflow
TMR1H = $17 ' these values are calculated for 4MHz
TMR1L = $B8 '
T1CON = %11110001 ' set internal clock, start timer, prescaler 1:8

INTCON= $C0 ' ENABLE INTERRUPTS
Counter=0
i = 0
_Loop:
'while true ' endless loop
BackupC = Counter ' save counter - interrupt might change it
WordToStr1(BackupC) ' split BackupC to digits

PORTB = M3 ' display digit
PORTA = 8 ' turn ones display on
delay_us(1000) ' wait for a while
PORTA = $00 ' turn all displays off
if BackupC >= 10 then' turn display on only in case upper digits are not equal to 0
PORTB = M2 ' display digit
PORTA = 4 ' turn tens display on
delay_us(1000) '
PORTA = $00 ' turn all displays off
End If

If BackupC >= 100 Then
PORTB = M1 ' display digit
PORTA = 2 ' turn hundreds display on
delay_us(1000) '
PORTA = $00 ' turn all displays off
End If

If BackupC >= 1000 Then
PORTB = M0 ' display digit
PORTA = 1 ' turn thousands display on
delay_us(1000) '
PORTA = $00 ' turn all displays off
End If
'Wend
goto _Loop
end.