8051 microcontroller programming:Timers-interfacing Timer0 and Timer1 together

July 01, 2016

Timers are one of the most important peripherals of 8051. There are two 16-bit counters present in 8051.

It is controlled using TMOD register.

C/T

The first four bits are for the Timer1 and the lower four bits are for the Timer0.

G- Gate bit for timer1.

0-TR1 should be made high starting the timer.

1-INT1 and TR1 should be HIGH for starting the timer.

C/T- Counter/Timer

0-Acts as timer .i.e. internal oscillator provides the clock.
1-Acts as counter .i.e. external crystal provides the clock.

M1,M0- Mode selectors.

M1	MO	MODE	FUNCTION
0	0	0	13-bit timer
0	1	1	16-bit timer
1	0	2	8-bit auto reload timer
1	1	3	Split timer

Timer 1 in mode 2 is used for serial communication.

Maximum count possible is in Mode-1, that is FFFF (66535).

Delay(microseconds)=1.085*(Final value-Initial value+1)

The counter counts from the value given in TH and TL registers to the maximum value.

When the timer reaches the maximum value the TF bit goes high.

ORG 0000H
SJMP MAIN
ORG 000BH
CPL P1.0
MOV TH0,#0A2H
MOV TL0,#0AAH
SETB TR0
RETI
ORG 001BH
CPL P1.1
MOV TH1,#01H
MOV TL1,#22H
SETB TR1
RETI
MAIN: MOV IE,#8AH
MOV TMOD,#11H
MOV TH0,#32H
MOV TL0,#0AAH
MOV TH1,#01H
MOV TL1,#22H
SETB TR1
SETB TR0
SJMP $
END