Timers 8051 microcontroller has two 16-bits built in timers.ppt

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1. 8051
TIMERS

4. TMOD REGISTER

7. 1514131211109 8 7 6 5 4 3 2 1 0
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1
0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0
0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1
…....….….….….….….…......................
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
Int Val
count
Max Val,
Roll off
(Hex.)
0000H
0001H
0002H
..
…
…
…
FFFFH
0000H

9. 1514131211109 8 7 6 5 4 3 2 1 0
X X X 0 0 0 0 0 0 0 0 0 0 0 0 0
X X X 0 0 0 0 0 0 0 0 0 0 0 0 1
X X X 0 0 0 0 0 0 0 0 0 0 0 1 0
X X X 0 0 0 0 0 0 0 0 0 0 0 1 1
…....….….….….….….…......................
X X X 1 1 1 1 1 1 1 1 1 1 1 1 1
X X X 0 0 0 0 0 0 0 0 0 0 0 0 0
Int Val
count
Max Val,
Roll off
(Hex.)
0000H
0001H
0002H
..
…
…
…
1FFFH
0000H

11. 7 6 5 4 3 2 1 0
0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 1
0 0 0 0 0 0 1 0
0 0 0 0 0 0 1 1
…......................
1 1 1 1 1 1 1 1
0 0 0 0 0 0 0 0
Int Val
count
Max Val,
Roll off
(Hex.)
00H
01H
02H
..
…
…
…
FFH
00H
TLX
TLX =THX
LOAD Init.
value from
THx to TLx

14. Mode 0:
Max value =(1FFF)h =(8191)d
(COUNT= MAX VALUE- INITIAL VALUE)
Time Delay = COUNTX (12/ Crystal Freq.)
Time Delay = 8191 X (12/ Crystal Freq.)
( If Crystal Freq. = 11.0952 Mhz)
Time Delay = 8191 X (12/ 11.0952 x 10^6.)
Time Delay =8.8 m sec

15. Mode 1:
Max value =(FFFF)h =(65535)d
(COUNT= MAX VALUE-INITIAL VALUE)
Time Delay = COUNTX (12/ Crystal Freq.)
Time Delay = 65535 X (12/ Crystal Freq.)
( If Crystal Freq. = 11.0592 Mhz)
Time Delay = 65535 X (12/ 11.0592 x 10^6.)
Time Delay =0.071 sec

16. Mode 2/3:
Max value =(FF)h =(255)d
(COUNT= MAX VALUE-INITIAL VALUE)
Time Delay = COUNTX (12/ Crystal Freq.)
Time Delay = 255 X (12/ Crystal Freq.)
( If Crystal Freq. = 11.0592 Mhz)
Time Delay = 255 X (12/ 11.0952 x 10^6.)
Time Delay =0.2 m sec

17. Max value =(FF)h =(255)d
(COUNT= MAX VALUE-INITIAL VALUE)
Time Delay = COUNTX (12/ Crystal Freq.)

Time Delay =( MAX VALUE-INITIAL VALUE)X (12 / Crystal Freq.)

Td = (MV-IV) * (12/ Fc)
Td *(Fc/12) = MV- IV
IV = MV - { Td *(Fc/12) }
Initial Value = Max.Value - { time delay * (crystal Freq/12)
(IV) dec=(IV)hex
Initial value in hexadecimal to be loaded to THx and TLx Register of the
timer - x choosen

19. TIMER
PROGRAMMING

22. 8051
P1.6

23. 8051
P1.6

24. 8051
P1.6
Th=0.5ms, Tlow = 0.5ms

25. 8051
P1.6
DC= 75 % [ DC =Ton/T, where T = ton+toff.]
TON=75%
TOFF = 25%

26. INTERRUPTS

27. 8051
P1.1

28. 8051
P1.1
Th=5us, Tlow = 5Us

30. 8051
INTERRUPTS

32. cont..

35. When an interrupt occurs, the updated PC is pushed on the stack and is loaded
with the vector address corresponding to the interrupt.
The table gives the vector addresses. The order of entries in the table is also the
order in which the 8051 will poll these in case of multiple interrupts.

43. Sequence of Events after an interrupt
When an enabled interrupt occurs,
1. The PC is saved on the stack, low byte first. This is because the stack grows
upwards in 8051.
2. Other interrupts of lower priority and same priority are disabled.
3. PC is loaded with the vector address corresponding to the interrupt. ---PGM--
When the handler executes ‘RETI”
1. PC is restored by popping the stack.
2. Interrupt status is restored to its original value. (Same and lower priority
interrupts restored to original status)

44. DIFFERENCE BETWEEN RET & RETI