Power up reset

[ShawnB]

Hi Acetronics,

My current port configuration setup:

'*** PIC16F886 CONFIGURATION *************************

OSCCON = %01100000

ANSEL = %00000011
TRISA = %11111111

ANSELH = %00000000
TRISB = %00000000

TRISC = %11111111

So I should look at adding PORTx = 0 before the TRISx register to clear the port register?

Is this good programming practice (newbe question)?

I have pull-down resistors on the input but not on the outputs, so I can look at adding those.

[ErnieM]

So I should look at adding PORTx = 0 before the TRISx register to clear the port register?

Is this good programming practice (newbe question)?

I have pull-down resistors on the input but not on the outputs, so I can look at adding those.

By all means clear the ports before changing TRISx. The MC data sheet on this part defines the port pins as UNDEFINED after power-up.

It is definitely good programming practice, even on parts where the data sheet says the pins should be in the state you think you want.

Output pull downs are probably the way to go, just make sure you have enough current to drive them, and they take enough current to actually pull down the input they drive.

[Acetronics2]

So I should look at adding PORTx = 0 before the TRISx register to clear the port register?

Is this good programming practice (newbe question)?

I have pull-down resistors on the input but not on the outputs, so I can look at adding those.

Hi, Shawn

Clearing PORTx is not the way ...

but you must set PORTx to get a SAFE and KNOWN state at your Program start ...

so, if you have a PNP transistor driving something ... it's driving port initial state MUST be a "1" state with a Pullup resistor ... for the transistor NOT to conduct.

I already had the "gag" with an electronic ignition :

@ Power UP the guy had programmed a CLEAR Port.

and after he had preset the Port pin to 1 ... as the transistor driven was a PNP ...


so, When turning the contact Key ... often an explosion occured in a cylinder : not so good , hey ???

The Good practice is to ensure a SAFE initial state ... processor placed or not.

Alain