I want to run a PIC from a 38 kHz crystal. The data sheet for the 16F84 states that for low frequency crystals, it may be necessary to insert a series resistor.
Does anyone know how to determine the value of this resistor? The one I intend to use has a 1 uW max drive level and an ESR of 35 k Ohm.
So do I assume that the drive level is V^2 * 35 k ?
sorry no idea.. but i have allways had good luck taking an oscillator and dividing it down..
right now i am using a 5MHZ and am dividing it down to somwhere around 500kHZ..
with more counters i have taken it down to a heart beat .. lol
have you got a scope? make a quick program to toggle a pin every 10 instruction cycles and have a look on the scope to see if the timing it right/wrong.
BTW, is your application timing dependant? if so perhaps a specialist timing IC might be better???
Thanks for the responses, but as I said in the original post, the 16F84 data sheet states that a series resistor is necessary, presumuably as too much drive power may shatter the xtal.
Thanks for the responses, but as I said in the original post, the 16F84 data sheet states that a series resistor is necessary, presumuably as too much drive power may shatter the xtal.
What page? I looked in the datasheet before I typed my response and didn't see anything to that effect. Just use the crystal with the necessary capacitors and then tell us if it doesn't work.
What page? I looked in the datasheet before I typed my response and didn't see anything to that effect. Just use the crystal with the necessary capacitors and then tell us if it doesn't work.
Mike, you may be right. I have the Microchip 16F84A "preliminary" data sheet DS35007A.
Page 22 under the heading of 6.2.1 Oscillator types Figure 6-2 shows the series resistor RS. But on re-reading note 2 the resistor "may be required for AT strip cut crystals"
However, the crystal I have states a max drive of 1 uW. So I would like to check the drive power.