Microprocessor Week 9: Timer and Counter

MICROCONTROLLER
MCS-51:
TIMER / COUNTER
Arkhom JODTANG
Civil Aviation Training Center

Timer / Counter
Contents
 Timer and Counter
 Timer Register
 Timer Mode
 Timer Mode 1
 Sample: Daley Programming
 Sample: Pulse generation programming
2

MCS51 Timer / Counter
 The 8051 has two timers/counters are Timer 0 and Timer 1
 Both of them can be used either as timers to generate a
time delay or as counters to count events from external
signal coming to microcontroller.
 By Set interval value, enable timer to start running while
monitoring overflow bit to know the completion interval.
3

Timer Register
4
 TMOD (Timer operation Mode) register
 TCON (Timer Control) register
 THx Register (TH1 for Timer 1, TH0 for Timer 0)
 TLx Register (TL1 for Timer 1, TL0 for Timer 0)

Mode 1 Equivalent circuit
5
Modified from http://blog.circuits4you.com/2015/07/programming-timers-on-8051.html
/ 12
THx TLx
Clock
Gen.
Machine Cycle

TMOD (Timer operation Mode) register
6
 Gate:
 “0” : enable timer by TRx bit
 “1” : enable timer by TRx bit with external signal at pin INTx
 C/T: Counter and Timer selector
 1 for Count signal from Tx Pin (Counter)
 0 for Count internal clock signal (Timer)
 M1: Mode bit 1 (MSB)
 M0: Mode bit 0 (LSB)
TMOD
Timer 1 Timer 0
Gate C/T M1 M0 Gate C/T M1 M0
0 0 0 1 0 0 0 0

Mode of Operation
8
 Mode 0: 13-bits
 THx (8-bits) and TLx (5-bits) combine as 13-bits
register
 Mode 1: 16-bits
 THx and TLx combine as 16-bits register
 Mode 2: 8-bit Auto reload
 THx is master value of TLx
0 1 1 0

Setting Mode Operation
9
0 1 0 1
Setting mode of operation by assign appropriate
value to TMOD register
 Timer 1 Mode 1
 MOV TMOD, #00010000B
 MOV TMOD, #10H
 Timer 0 Mode 1
 MOV TMOD, #00000001B
 MOV TMOD, #01H

Example 9.1
10
TMOD
x x x x x x x x
Find the value for TMOD if we want to program
Timer 0 in mode 1, count from internal clock source,
and use instructions to start and stop the timer.
Timer 1 in mode 2, count from external and start
counting by instruction.
01100001

Mode 1 Equivalent circuit
11
Modified from http://blog.circuits4you.com/2015/07/programming-timers-on-8051.html
/ 12
THx TLx
Clock
Gen.
Machine Cycle

Example 9.1
12
TMOD
Timer 1 Timer 0
0 0 0 0 x x x x
Timer 0 in mode 1, count from internal clock
source, and use instructions to start and stop the
timer.
Solution:
 Timer 0, So, we care only Timer 0 Nibble

Example 9.1
13
TMOD
Timer 1 Timer 0
0 0 0 0 x x 0 1
and use instructions to enable the timer.
Solution:
 Timer 0: So, we care only Timer 0 Nibble
 Mode 1: M1 = 0, M0 = 1

Example 9.1
14
TMOD
Timer 1 Timer 0
0 0 0 0 x 0 0 1
and use instructions to enable the timer.
Solution:
 Mode 1: M1 = 0, M0 = 1
 Internal Clock: That mean Timer. So, C/T = 0

Example 9.1
15
TMOD
Timer 1 Timer 0
0 0 0 0 0 0 0 1
Find the value for TMOD if we want to program Timer 0
in mode 1, count from internal clock source, and use
instructions to enable the timer.
Solution:
 Mode 1: M1 = 0, M0 = 1
 Enable by TR0 bits: Gate = 0

Example 9.1
16
TMOD
Timer 1 Timer 0
0 0 0 0 0 0 0 1
Find the value for TMOD if we want to program Timer 0 in mode 1, count from
internal clock source, and use instructions to enable the timer.
Solution:
 Mode 1: M1 = 0, M0 = 1
 Enable by TR0 bits: Gate = 0
Answer: Value of TMOD is #00000001B or #01H
(Use instruction MOV TMOD, #01H)

TCON (Timer Control register)
17
 TF1: Timer 1 Over Flow bit
 This bit will set when timer is over flow
 TR1: Timer 1 Enable bit
 Start running of Timer 1
 TF0: Timer 0 Over Flow bit
 This bit will set when timer is over flow
 TR0: Timer 0 Enable bit
 Start running of Timer 0
 IE1, IT1, IE0, IT0 will describe in next chapter
TF1 TR1 TF0 TR0 IE1 IT1 IE0 IT0
0 0 0 1 0 0 0 0

Mode 1’s Operation
18
THx TLx
0 0 0 1 0 0 0 0 0 1 0 1 1 0 0 1
 THx and TLx store start value
 Timer operation always count-up (increase) on [THx, TLX] each machine cycle
 SETB TRx instruction to start running timer
 Over flow when Increase FFFF to 0000
 Interval value = FFFF – [TH,TL]
 FFFF give minimum interval time
 0000 give maximum interval time
 Example:
 MOV TH0, #22H
 MOV TL0, #00H
 ; Then interval is FFFF – 2200 = DDFF Machine Cycle.
 Tips: Monitor TFx with instruction
 “MonitorLable : JNB TFx, MonitorLable”

Example 9.2
19
Calculate amount of time delay in the DELAY subroutine below
generated by the timer. Assume that XTAL = 11.0592 MHz.
Delay:
MOV TMOD, #01
MOV TL0, #0F2H
MOV TH0, #0FFH
SETB TR0
MonitorTX : JNB TF0, MonitorTX
CLR TR0
CLR TF0
RET

Example 9.2
20
Solution:
The timer works with a clock frequency of 1/12
of the X’TAL frequency; therefore, we have
11.0592 MHz / 12 = 921.6 kHz as the timer
(Machine Cycle) frequency.
As a result, each clock has a period of T = 1 /
921.6 kHz = 1.085 (is. In other words, Timer 0
counts up each 1.085 s resulting in delay =
number of counts x 1.085 s.

Example 9.2
21
Solution:
As the timer counts up, it goes through the
states of FFF3, FFF4, FFF5, FFF6, FFF7, FFF8,
FFF9, FFFA, FFFB, FFFC, FFFD, FFFE, and
FFFFH. One more clock rolls it to 0000, raising
the timer flag (TF0 = 1). At that point, the JNB
instruction falls through.
Timer 0 is stopped by the instruction “CLR TRO”.
The DELAY subroutine ends

Example 9.2
22
Place Machine cycle to the code:
Delay:
MOV TMOD, #01 2
MOV TL0, #0F2H 2
MOV TH0, #0FFH 2
SETB TR0 1
MonitorTX : JNB TF0, MonitorTX 14
CLR TR0 1
CLR TF0 1
RET 2
Total = 25

Example 9.2
23
From total machine cycle used was 25 machine cycles.
25 x 1.058 s. = 27.125 s.
So, This subroutine generate delay for 27.125 s.
Conclusion: Total Machine cycle to overflow is
Machine Cycle = 1 + FFFF – Interval (TH,TL) value

Workshop 9.1
24
Calculate amount of time delay in the DELAY subroutine below
generated by the timer. Assume that XTAL = 22.1184 MHz.
Delay:
MOV TMOD, #01
MOV TL0, #034H
MOV TH0, #012H
SETB TR0
MonitorTX : JNB TF0, MonitorTX
CLR TR0
CLR TF0
RET

Example 9.3
25
Connect Port 3.0 with
Input Switch and Port 1.0
with LED Display
Write Program for MCS51
to Turn ON LED for 2
Second after user press
input switch.
Show calculate delay
generate by MCS51.
Assume that X’TAL =
11.0592 MHz.
Start
TMOD
End
P3.0
= 1
ON
Display
Delay 2
Seconds
OFF
Display
WaitSW:
R3 =33D
DJNZ R3, Loop
Delay
Loop:

Example 9.3
26
Connect Port 3.0 with
Input Switch and Port
1.0 with LED Display
From code below
calculate delay
generate by MCS51.
Assume that X’TAL =
11.0592 MHz.
MOV TMOD, #10H ; Set Timer Mode
CLR P1.0
WaitSW: JB P3.0, WaitSW
SETB P1.0
ACALL Delay
CLR P1.0
SJMP $
Delay:
MOV R3,#31D
MainProcess:
MOV TL1,#08H
MOV TH1,#1H
SETB TR1
Monitoring: JNB TF1, Monitoring
CLR TR1
CLR TF1
DJNZ R3, MainProcess
RET
END

DJNZ (Sample)
 ; DJNZ is very convenion for
 ; specified number of turn for
some process.
 MOV R3,#31D
 Loop:
 ; Process here
 DJNZ R3, Loop
 END
28
Start
R5 =10D
End
Loop:
DJNZ R5, Loop
Process

Example 9.4
29
From code below calculate frequency of signal generate by MCS51. Assume that X’TAL =
11.0592 MHz.
MOV TMOD, #10H
Loop:
CPL P1.1
ACALL Delay
JMP Loop ; All Loop All Delay + 7 = FF04H = 65286D Machine cycle
Delay:
MOV TL1,#08H
MOV TH1,#1H
SETB TR1
Monitoring: JNB TF1, Monitoring
CLR TR1
CLR TF1
RET ; All Delay code FEFF
END

Example 9.5
30
Write assembly
program for MCS51
to generate Pulse
signal with duty cycle
20% to pin P1.1
MOV TMOD, #10H
Loop: SETB P1.1
ACALL DelayON
CLR P1.1
ACALL DelayOFF
JMP Loop
DelayON: MOV TL1,#00D
MOV TH1,#236D ; 256-20
SETB TR1
MonitoringOn: JNB TF1, MonitoringOn
CLR TR1
CLR TF1
RET
DelayOFF: MOV TL1,#00D
MOV TH1,#176D ; 256-80
SETB TR1
MonitoringOff: JNB TF1, MonitoringOff
CLR TR1
CLR TF1
RET
END

Microprocessor Week 9: Timer and Counter

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