Pic16F628 problem when Oscilloscope disconnected

[Stanley]

Hi.
Have a strange problem whit my Pic16F628 communicating on 9600 8N1 whit a mobile phone running at 3.6V.

When I have the oscilloscope connected to the clock out everything is working find but when I disconnect the scope I only receve garbage from the phone. Anyone know what could be wrong??

Settings:

#use delay(clock=4000000)
#fuses NOWDT,INTRC, PUT, PROTECT, NOBROWNOUT, MCLR, NOLVP, NOCPD

#use rs232(baud=9600,xmit=PIN_B6,rcv=PIN_B7, stream=PHONE) // For communication to phone. Use Software

setup_counters(RTCC_INTERNAL,RTCC_DIV_1);
setup_timer_1(T1_DISABLED);
setup_timer_2(T2_DISABLED,0,1);
setup_comparator(NC_NC_NC_NC);
setup_vref(FALSE);

[Adrianf]

Just a guess but mobiles give off a fair bit of RF. Have you tried a capacitor of a similar value to the scope probe on the same pin to ground? Might give you a pointer. I've had circuits do similar where the scope has damped out oscillations.

[PCM programmer]

My first thought was a missing ground connection or the MCLR
pin was left unconnected. Upon researching it, I found this
post at Microchip, which yes, does end up being a messed up
MCLR circuit. Check that first.
http://forum.microchip.com/tm.asp?m=18330

[Stanley]

Thanks for the replay.
I found out that my scope have an input at 1Mohm and 22pf

-Stan.