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Floating pin causes reset.

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qtommer

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hi.

I have established communcication between a PIC and a Handphone. I realized that whenever an I/O pin (which I set HIGH as a RTS signal) is left floating (handphone gets disconnected in operation midway), the PIC will reset and my system goes back to trying to reinitiate communication again.

I find that this is actually very useful if manipulated well to detect the existence of connections or not so I just want to verify if what I am experiencing now has any theory to why it behaves so..

Anyone know why ??:)

thanks!
 
nope my board is actually fabricated on PCB and MCLR is tied to 5V through a pull up resistor...when I removed the line of code (bsf PORTB,1) to make the RTS high, the system did not reset but just carried on as usual.the reset happened 10 out of 10 times when the line of code was there..

however, your experience surpasses my little experiment...so i guess it SHOULD be a programming error:) so i guess the conclusion is no such thing should happen rite?
 
The added line of code may push the instructions down one line and cause a jump-relative to create the problem or the WDT may cause the reset. Put a NOP in place or another instruction and see what happens. What is on the pin?
A cap on the pin may cause the power to dip and reset the chip. Do you have 10u and 100n across the chip? Or it could be long lines to the chip. Or you may be controlling something that is dipping the supply.
What is the chip and do you have external Xtal or RC?
 
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hi thanks for the replies..

B1 feeds to the input of a MAX232 TTL driver.

and the chip i use is the 876A and I have an external 4MHz XTAL...i have decoupling caps for both my 876a and MAX232 near the power rail lines...
i would post my code but it really is too long (nearly 2K) ...
 
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