Adolfo Cobo (Ingenieria Fotonica) wrote:
>
>  Hello to all,
>   I need advice with a "problem" I've found: I'm working in a project with
> a PIC16F84-04/P that will be connected to a Pc using the parallel port. An
> input pin (RA1) of the PIC is connected to an out (D0) of the LPT port,
> and, because the circuit may be connected or not, I decided to add a
> pull-up resistor of *330K* to the pin, forcing a high level when the PC is
> not connected.
>   And now the problem: the current from the pin of parallel port at logic
> level high seems to feed the entire PIC circuit, because it runs even
> without power. The voltage across the pull-up resistor is 1.2V, so I supose
> that the PIC chip is consumming 3.6 microAmps. Of course, I'm not using the
> SLEEP mode and there is not short-circuits in the PCB. May be that the
> current flows internally from the RA1 ping to Vcc??? It seems very strange,
> Any suggestions???
>  Thanks in advance.
>
>  -----------------------------------------------------------------------
> |         Adolfo Cobo Garcia  -  UNIVERSIDAD DE CANTABRIA               |
> |    E.T.S.I.I. y Telecomunicacion, Grupo de Ingenieria Fotonica        |
> |        Avda. Los Castros s/n  E-39005  Santander  SPAIN               |
> |  Tfno. +34-42-201539  Fax +34-42-201873  Email: acobo@teisa.unican.es |
>  -----------------------------------------------------------------------

Remember the internal protection diodes!!