8-bit Microcontrollersのトピック9SO8QG8 CLOCK

9SO8QG8 CLOCK

euge — Thu, 03 Jan 2008 21:57:06 GMT

Í'm testing a 9S08QG8 by first time with a 4MHz oscillator in FBE mode.

On Data sheet and other freescale documents

fbus=(fext*1/BDIV)/2 = 1/tcyc where tcyc is time machine cycle

I used BDIV=1 ==> divide by 2

Then fbus=4MHz/4=1MHz ==> tcyc=1us

I tryed to check this, generating a square wave with

C code Assembler code

for(; { PTBD_PTBD2=1; 44: PTBD_PTBD2=1; 0014 1400 BSET 2,_PTBD //2 cycles _asm NOP 45: _asm NOP 0016 9d NOP //1 cycle PTBD_PTBD2=0; 46: PTBD_PTBD2=0; 0017 1500 BCLR 2,_PTBD //2 cycles _asm NOP 47: _asm NOP 0019 9d NOP //1 cycle

__RESET_WATCHDOG(); // feeds the dog } // loop forever

If tcyc is 1 us I would have to obtain a 3 us period square wave but I obtain a 6 us period.

Maybe fext is fcrystal/2 and this information is not well documented or tcyc is not 1/fbus.

Maybe some of you with more experience have a response.

I regulary use 9S12, GP32 and QT2 MCUs and I never had this discrepancy.

Best Regard

Re: 9SO8QG8 CLOCK

Ake — Thu, 03 Jan 2008 23:11:02 GMT

Hello,

I wrote your code and tested it,

void qc8intosc(void) {
SOPT1_COPE = 0;//turn off the watchdog
PTBDD_PTBDD6 = 1;

for(; { //this loop takes 13 clock cycles to execute
PTBD_PTBD6 = 1;
PTBD_PTBD6 = 0;
} /* loop forever */
}

It will oscillate at 304 kHz.
As the loop takes 13 clocks to execute, this means that the fOP is 13 * 304 kHz = 3.95 MHz.

I have not got an external oscillator, so I cannot test your conditions, but maybe this helps?

Regards,

Ake

Re: 9SO8QG8 CLOCK

bigmac — Fri, 04 Jan 2008 23:39:15 GMT

Hello,

Further to the comments by Ake, the number of cycles required by BSET or BCLR instructions will be 5 cycles, and not 2 cycles. Additionally, you did not allow for __RESET_WATCHDOG() macro, (assume 4 cycles), and for a BRA instruction to provide a continuous loop (3 cycles). This would mean that your code should loop every 19 cycles, (assuming no interrupts). Because of the additional overheads, the waveform will be asymmetric.

Regards,

Mac

Re: 9SO8QG8 CLOCK

euge — Sat, 05 Jan 2008 00:46:29 GMT

Ake, Bigmac Thank both for your time thinking about my doubts. The solution is that BSET or BCLR use 5 cycles not 2 cycles. I thought that each opcode and each operand corresponds to a cycle. That occurs when you do not consult the manual!!!!!!!! Best Regards

Eugenio

Re: 9SO8QG8 CLOCK

euge — Sat, 05 Jan 2008 00:47:50 GMT

Ake, Bigmac

Thank both for your time thinking about my doubts.
The solution is that BSET or BCLR use 5 cycles not 2 cycles.
I thought that each opcode and each operand corresponds to a cycle.
That occurs when you do not consult the manual!!!!!!!!
Best Regards!!!!