[SOLVED] 8051 timer configuration

[ark5230]

I am trying to produce delay of 1/20 s (50 ms) using Timer/counter 0.
Crystal frequency is 11.0592 MHz and machine cycle is 11.085µs.
for 50ms the machine cycles required is 46079 decimal.
The counter is to be loaded with 65536-46079=19457=4C01Hex
TH0=04CH and TL0=01H.

SETB TR0 initiates timing and Polling TF0 gives the end of the required time.

Now the problem is IF Timer 0 is to be configured for the above purpose, What should be TMOD value?
TMOD = 01010001B configures this but also configures Timer 1 as counter !!
If timer 1 is not to be configure what should be the TMOD value.
A simple explanation of these setting will be of help.

        MOV TMOD,#01010001B ; TIMER CONFIGURATION
        MOV TH0,#4CH     ; VALUE IN TH0 FOR 1/20 S DELAY
        MOV TL0,#01H     ; VALUE IN TL0 FOR 1/20 S DELAY
        SETB TR0         ; START TIMER (FOR 1/20 S DELAY) 
        JNB TF0,$        ; WAIT TILL COUNTING IS OVER
        CLR TF0          ; CLEAR TIMER FLAG TF0
        RET

 

[raymic]

If you are not using Timer1 have to put 0 in high nibble of TMOD. Try the following, hope will be useful.

  org 0000h                                      ;reset
  jmp init_prog
  org 000bh                                      ;timer0
  jmp t0_isr
  org 0100h                                      ;main code starts somewhere else
init_prog:    
  mov  ie,#10000010b                       ;enables timer0 interrupt
  mov  tmod,#01h                            ;TMOD = 0000 0001 which means in low nibble for timer0 mode 1 (16 bits) and soft trigger
  mov  th0,#4ch                               ;50ms using clock = 11.059 Mhz
  mov  tl0,#00h
  setb  tr0                                        ;triggers timer0
  jmp   $
t0_isr:
   mov  th0,#4ch                               ;recharge 50ms 
   mov  tl0,#00h
   ;INSERT YOUR CODE HERE ......
   reti                                                ;you don't have to clean the flag TF0 before exit
end

 

[ark5230]

Actually I want to keep it simple without interrupts.
The TMOD value should be 0000 0001 instead of 01010001B.
I will try to understand this. The details in datasheet are too technical!
Thanks for help, I would appreciate if some one could explain this TMOD configuration issue.

 

[raymic]

more help: 8051 timer configuration

OK, is not a problem.
Every nibble of TMOD have the following bits GATE, C/T and M1M0.
Configurating TMOD = xxxx 0001 means GATE = 0, the timer will start by soft with instruction setb TR0 C/T = 0 means working as timer0 with the clock pulses coming from your 11.059Mhz and M1M0 = 01 means that you will use the full 16 bits of timer0 with the calculations you already made. The don`t care bits in higher TMOD means the same for timer1. Usually timer1 is involved with serial port, where the regular configuration is TMOD = 21h, the 2(0010) means autorecharge mode of 8 bits for baud rate in timer1, bibliography have the table constants for TH1 = TL1 according to your 11.059Mhz clock. the 1(0001) remains timer0 being a timer of 16 bit for general purpouse.

 

[ark5230]

Thanks a lot, precisely this is what I was looking for.