3.4. Timer/ Counter Mode 3 : Two 8 bit
Timer 1 in Mode 3 simply holds its count. The effect
is the same as setting TR1=0.
Figure 3.4. 1. Timer/ Counter 1 mode 3
Timer 0 in Mode 3 establishes TL0 and TH0 as two separate
counters. The logic for Mode 3 on Timer 0 is shown in Figure 10. TL0
uses the Timer 0 control bits: C/T, GATE, TR0, INT0, and TF0. TH0 is
locked into a timer function (counting machine cycles) and takes over
the use of TR1 and TF1 from Timer 1. Thus, TH0 now controls the “Timer
Mode 3 is provided for applications requiring an extra 8-bit timer on
the counter. With Timer 0 in Mode 3, an 80C51 can look like it has three
Timer/Counters. When Timer 0 is in Mode 3, Timer 1 can be turned on
and off by switching it out of and into its own Mode 3, or can still
be used by the serial port as a baud rate generator, or in fact, in
any application not requiring an interrupt.
3.4.1. Timer/ Counter acts as Counter Mode
3 with output LED
A simple way to detect wheater the counter counting or not
is by using 8 LED as output of P0.0 trough P0.7.
Figure 3.4.1. Get data counter out to LED
Build the circuit as shown in figure 3.4.1. As you seen on figure 3.4.1.
P0.0 trough P0.7 is connected to LED. Remember, that all we want to do
with this lesson is count the pulse and display to LED
In this step, you must tipe the assembly program to make your Timer
get action, we assume that you have already known the editor, we used
MIDE-51 to edit the program. ( Download File : exp341.zip
Start: Mov TMOD,#01110000b ; mode 3 counter 8 bit timer 1
Setb TR1 ; TR1 = 1, start counting
Get: Mov A, TL1 ; A = TL1
Mov P1, A ; P1 = A
Sjmp Get ; Looping Forever
Safe your assembly program above, and name it with timer3.asm (for example)
Compile the program that you have been save by using MIDE-51, see the
Download your hex file ( timer3.hex ) into the microcontroller
by using Microcontroller ATMEL ISP software, see the instruction.After
download this hex file you'll see the action of Timer( of course if
your cable connection and your program are corrected ).
questions and discussion about this topic