Frequency for square wave

Cenlasoft

Hello,
Bean gave me some code:
DEVICE SX28,OSCHS2,TURBO,OPTIONX,STACKX
FREQ 50_000_000, 34_000_000

OutPin PIN RA.0 OUTPUT

INTERRUPT NOCODE 2_000_000
OutPin = ~OutPin
RETURNINT

PROGRAM Start

Start:
END

It worked well, I want to know if I can go as low as 53 khz?
Will it work for a 4MHz resonator as well?
I apologize for the simple questions.
Thank you,
Curtis

JonnyMac

Remember that Period = 1 / Frequency -- and you need to split the period to get a square wave. Change your code to this:

INTERRUPT NOCODE 26_500
  OutPin = ~OutPin
  RETURNINT

It probably won't be perfect, but should get you close.

Cenlasoft

Thanks for the info, I tried the code below and it gave me a 54.6 khz square wave signal on my scope. I will tweak it to get my 53 khz square wave.

INTERRUPT NOCODE 106_000
OutPin = ~OutPin
RETURNINT

My questions are:
1. I will be sending the square wave to a tank circuit (coil and capacitor). LC tank circuits can produces high voltages and current. Should I put a resistor or diode to protect my sx28 pin?
2. Is there is any code I can use to keep the frequency stable? I am a beginner in the sxb.
3. I will be reading the voltage on the coil using a voltage divider and ADC0831 later. Any thoughts are appreciated.
Thanks,
Curtis

Bean

The output frequency is dependent on the frequency that is clocking the SX, and the ratio of SX clock to output frequency.

For example assume you are using a 4MHz resonator. The resonator could be off by +/- 100ppM or so.

Then you have the ratio. 4_000_000 / 106_000 = 37.7, so this should get rounded to 38. So 4_000_000 / 38 = 105_263 / 2 = 52631 Hz.

Bean.

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Cenlasoft

Thanks Bean,
I understand the concept now. I can now experiment with my tank circuit and my experiments.
Curtis