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How can I count 1 second using an 8051 at 22Mhz??

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Todi

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Hello everyone!

So, I'm having lessons about computer architecture and the examples are passed using experiments with an ATMEL 8051 at 22Mhz.

I'm initializing the TIMER0 in 16-bits mode and I'm trying to do the clock count 1 second after another. Knowing this, what I'm doing is:

22Mhz / 12 = 1,833333Mhz x 10^6 = 1833333Hz
1 / 1833333Hz = 0,5us

And I'm stuck in here... what I have to do to know how much times I have to count to 1 second? I mean, what number I have to initiate the TH and TL? And how many times I have to count?

Thank you all!

PS.: I'm using Assembly!
 

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    IanP

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With 22MHz the time unit is not 0.5us but roughly 0.545us
To get 1ms delay the reload values are:
65536-1835=63701 => F8 D5
(1ms ≈ 1835 * 0.545us)

Use Timer 0 of 8051 in MODE1 (16 bit timer) ...

Code: 
DELAY: MOV TMOD,#00000001B // Sets Timer 0 to MODE1 (16 bit timer)
       MOV TH0,#0F8H // Loads TH0 register with F8H
       MOV TL0,#0D5H // LOads TL0 register with D5H
       SETB TR0 // Starts the Timer 0
HERE: JNB TF0,HERE // Loops here until TF0 is set (ie;until roll over)
      CLR TR0 // Stops Timer 0
      CLR TF0 // Clears TF0 flag
      RET
The above delay routine can be looped 1000 times in order to get a 1000mS=1s delay ...

:wink:
IanP
 

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