If-statement - Condition depending on output pin

[eng1]

Below I include simplified C code for a function 'read_ADC'.

RB0 is configured as output pin.

The function has to determine the state of RB0; then RB0 is cleared inside this function and other operations with ADC, etc. are implemented.
Then, RB0 must be restored, according to its original state.

void read_ADC()
{

	if(RB0)	// CORRECT ??
		RB0_state = 1;
	else
		RB0_state = 0;


	RB0 = 0;

	DelayMs(200);    // 200 ms
	
	Read_Ch(1);      // read ADC

	RB0 = RB0_state;  // restore RB0
}

Is it ok to check the state of RB0 (which is configued as outout pin) directly on the PORTB register?
The program runs correctly as I expected with the hardware. Do you see anything wrong/drawbacks with this solution? Of course I could update the variable RB0_state throughout the program, anywhere RB0 is changed; but this would require additional works and tests.

 

[edeca]

You don't say whether you are using an 18F or 16F series PIC, the answer may be a little different. It is perfectly fine to check port bits to see what the current output state is.

You can simplify your code to this though:

void Read_ADC()
{
	char original_state = RB0;	// Save original state
	RB0 = 0;			// Force pin low
	DelayMs(200);			// Delay
	Read_Ch(1);			// Read ADC
	RB0 = original_state;		// Restore original state
}

 

[eng1]

Thank you for your comments.

I am using a PIC16F. And of course I'll simplify the first lines as you have suggested.

 

[edeca]

OK, on a 16F the only thing you can do is read from the port itself (unlike the 18F, which has a data latch). You should also be aware of the read-modify-write problem just in case (see ).

As you rightly said earlier in the thread a good solution is to have a variable that keeps track of the current state of RB0 throughout the code.