Generate 2KHz by timer interrupt

alanlai1 · ‎2004-06-21

Posted on June 22, 2004 at 05:11

alanlai1 · ‎2004-06-14

Posted on June 14, 2004 at 14:09

Dear Sir ~

I am using ST6242, using interrupt to generate the toggle frequency.

(Target = 2kHz square wave for buzzer).

But I can not get the excected frequency.

My setting:

TSCR = 01101XXXB (XXX = PS0:2)

PSC = 0XXXXXXXB (XXXXXXX=)

TCR = 00000001B

My expect and determination:

Shortest Interrupt interval should be = 1 / (4Mhz / 12 / 1 ) = 3us

/ 12 means divide by 12 (refer to ST6242 spec page 18/70)

/128 means divide by 128 (refer to ST6242 spec page 41/70)

Shortest square freq = 1 / [3us (Hi) + 3us (Lo)] = 166kHz

PS(0:2)=000,PSC(0:7)=00000000>Result Freq=166kHz,interval=3us

My result:

PS(0:2)=000,PSC(0:7)=00000000>Result Freq=500Hz, interval=843us

PS(0:2)=001,PSC(0:7)=00000000>Result Freq=309Hz, interval=1.6ms

PS(0:2)=010,PSC(0:7)=00000000>Result Freq=158Hz, interval=3ms

PS(0:2)=011,PSC(0:7)=00000000>Result Freq=80Hz, interval=6ms

PS(0:2)=100,PSC(0:7)=00000000>Result Freq=40Hz, interval=12ms

PS(0:2)=101,PSC(0:7)=00000000>Result Freq=800Hz, interval=562us

PS(0:2)=110,PSC(0:7)=00000000>Result Freq=1.2kHz, interval=386us

PS(0:2)=111,PSC(0:7)=00000000>Result Freq=1.0kHz, interval=456us

In my testing above, I cannot find a setting can meet my expectation.

Is it my concept wrong? Can you please help in coding?

My Tools=ST6240B-EMU2, Compiler=RIDE

Thanks

Best Regards

Lai

marco32 · ‎2004-06-21

Posted on June 22, 2004 at 05:11

With the TCR you can the 500Hz multiply by 4! so you can make 2Khz.

But for the calculation for the timers, i use always an excel sheet. It's an automatic calculation after delay time insertion.

I attached the excel sheet.

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