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ICSP Question

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Roger Harrold

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Can anyone tell me what happens to general purpose digital I/O lines during ICSP programming?
Not the ICSP data/clock lines, but other I/O. Are they low, high, floating?
 
Roger Usually after the ICSP program reset I/O are all input , and presumably during loading , however I have seen some ports show output activity during program, especially the UART pins...

We are talking PIC here ..?
 
Last edited:
"We are talking PIC here ..? "
Yes, sorry, should have been more specific. PIC18F1320

My application has the PWM pins driving an H-Bridge motor driver.
The motor goes to full speed during programming, and given the replies here I suspect it is because
the pins are inputs and floating, so the H-Bridge pins are undefined. I'll trying grounding them via
10k resistors so that go to 0v during programming.

Thanks for the replies.

Roger
 
If the H-bridge used not enable and the outputs were really TTL compatable, float high you would not have that problem.

The ULN2003 is an interesting device because when the inputs are open, the output is effectively low. Low is low and high is high. So, this solves the problem on start-up where the output is defined as an input.

There is another CMOS interface chip that does wierd, but predictable things with open CMOS inputs. Something like --- it maintains the previous state when the input tri-states.
 
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