TIMER PROGRAMMING
(Toggle LED using timer programming ON time delay greater than 3 times OFF time delay)
v What is timer?
Timer is a clock that controls the sequence of an event while counting in fixed intervals of time. A Timer is used for producing precise time delay. Secondly, it can be used to repeat or initiate an action after/at a known period of time. This feature is very commonly used in several applications. An example could be setting up an alarm which triggers at a point of time or after a period of time.
v Types of timer?
Two types of timer in 8051
Ø Timer0
Ø Timer1
Timer0 register
|
D15
|
D14
|
D13
|
D12
|
D11
|
D10
|
D9
|
D8
|
D7
|
D6
|
D5
|
D4
|
D3
|
D2
|
D1
|
D0
|
Timer1 register
|
D15
|
D14
|
D13
|
D12
|
D11
|
D10
|
D9
|
D8
|
D7
|
D6
|
D5
|
D4
|
D3
|
D2
|
D1
|
D0
|
TMOD register
|
GATE
|
Timer/counter
|
M1
|
M0
|
GATE
|
Timer/Counter
|
M1
|
M0
|
|
GATE
|
Gate=0 Internally run timer
Gate=1 External pin are used for timer run
|
|
|
TIMER/COUNTER
|
C/T=0 for Timer mode
C/T=1 for Counter mode
|
|
|
MODE
|
|
|
|
M1
|
M0
|
Mode description
|
|
0
|
0
|
13 bit timer/counter mode
THx= 8 bit
TLx= 5 bit
|
|
0
|
1
|
16 bit timer/counter mode
THx=8 bit
TLx= 8 bit
|
|
1
|
0
|
8 bit auto reload mode
THx=TLx
|
|
1
|
1
|
Split mode
|
TCON register
TF1 = Timer1 overflow flag
TR1 = Timer1 run flag
TF0 = Timer0 overflow flag
TR0 = Timer0 run flag
Timer calculation
Clock frequency of atmel microcontroller = 11.0592 MHZ
Time period =1/11.0592
Time period = 1.085 microsecond
For 5 ms second delay generate
=5 ms/ 1.085 us
=4608
For TH and TL value = 65536 – 4608
= 60927
60927 convert into hex value = EDFFh
TH=EDh
TL=FFh
No comments:
Post a Comment