running with external clock source trouble - DS1077
simon
Posts: 20
Hi!
My sx52 prototype board is running with a normal crystal @20mhz.
I connected the crystal to OSC1 & OSC2, added 2 small capacitors to GND and the
1 MOhm resistor between OSC1 and OSC2.
This setup runs fine @20Mhz and my test Program (basically a loop)
is producing a 1 second on/off at PORTD.
Now i removed the crystal and replaced it with a external clock source (50Mhz).
I left the capacitors and the 1MOhm resistor in place and connected the
ext. clock to OSC1:
Now my Program seems to run at 25Mhz [noparse]:([/noparse]
@20 mhz my loop takes 1,000s and it takes
now 0,800s -> 25Mhz (@50Mhz it should take 0,4s)
Do the capacitors and the resistor cause this trouble ?
But why is it diveded exactly by 2 ?
I need to know it before i remove them ...
Unfortuantly my oscilloscope is limited to 0,5 Mhz so
i can not test the external source directly.
My external clock source is a DS1077-50 preprogrammed to 50 Mhz and
with a 40 / 60 duty cycle (is this ok ? i was unable to find it in the sx52 manual).
I am running the sx in HS3 Mode.
Any Ideas ?
Thank you very much.
Bye, Simon
Post Edited (simon) : 9/10/2004 3:07:51 PM GMT
My sx52 prototype board is running with a normal crystal @20mhz.
I connected the crystal to OSC1 & OSC2, added 2 small capacitors to GND and the
1 MOhm resistor between OSC1 and OSC2.
This setup runs fine @20Mhz and my test Program (basically a loop)
is producing a 1 second on/off at PORTD.
Now i removed the crystal and replaced it with a external clock source (50Mhz).
I left the capacitors and the 1MOhm resistor in place and connected the
ext. clock to OSC1:
OSC1 o--+---------------------o << ext clock
= 15pf |
GND1 o--+ [noparse][[/noparse]] 1Mohm
= 15pf |
OSC2 o-------------+
Now my Program seems to run at 25Mhz [noparse]:([/noparse]
@20 mhz my loop takes 1,000s and it takes
now 0,800s -> 25Mhz (@50Mhz it should take 0,4s)
Do the capacitors and the resistor cause this trouble ?
But why is it diveded exactly by 2 ?
I need to know it before i remove them ...
Unfortuantly my oscilloscope is limited to 0,5 Mhz so
i can not test the external source directly.
My external clock source is a DS1077-50 preprogrammed to 50 Mhz and
with a 40 / 60 duty cycle (is this ok ? i was unable to find it in the sx52 manual).
I am running the sx in HS3 Mode.
Any Ideas ?
Thank you very much.
Bye, Simon
Post Edited (simon) : 9/10/2004 3:07:51 PM GMT
Comments
Ok, forget my question ...
I found out that the external clock source has a built in divider.
The output is divided by two ...
I need to clear the DIV1 via i2c ...
Now it is working as expected
Bye, Simon
Post Edited (simon) : 9/10/2004 8:46:23 PM GMT