In addition to a current limit on individual I/O pins there are current
limits for banks of pins.  For the 16F84 they are given in section 10.0 of
the Datasheet.
Max current sunk by PORTA          80mA
Max current sourced by PORTA       50mA
Max current sunk by PORTB          150mA
Max current sourced by PORTB       100mA

These are "Absolute Maximum Ratings".

I don't have the 16C7x datasheet handy, but IIRC, they are specified in two
sets of banks.

There is also a spec for max power dissipation for the chip given which
covers overall current handling capability - 800 mW for the 16F84.

Hope this helps,
Jonathan

> -----Original Message-----
> From: Andres Tarzia [SMTP:ATarzia@SMART.COM.AR]
> Sent: Wednesday, October 13, 1999 7:43 AM
> To:   PICLIST@MITVMA.MIT.EDU
> Subject:      Maximum current draw from a given PIC
> Sensitivity:  Private
>
> Hi all,
>
> Most PICs are rated to being able to source up to 20mA and to sink up to
> 25mA at any pin. I understand that this is an Absolute Maximum Rating that
> one cannot stress.
>
> Now, keeping into the safe side, say that I want to source 15mA from ALL
> output pins of a 16F84. Having up to 13 outputs, this would mean a total
> of
> nearly 200mA out of the chip. The situation worsens if I choose to use a
> 16C73, for example, with 22 output pins ALL sourcing 15mA for a total of
> 330mA. For a 16C74, with 33 output pins, you go into the 1/2 Amp range...
>
> Ok, so far so good, one cannot do that. So the question is: How do I
> compute
> the maximum current a given chip can source at a time? I need to drive
> several charges at (possibly) the same time and I am afraid of overloading
> or overheating the PIC. I guess that if I find that it is too much for the
> PIC I'd have to use transistors for driving my output charges.
>
> Thank you in advance.
>
> Regards,
> Andres Tarzia
> Technology Consultant, SMART S.A.
> e-mail: atarzia@smart.com.ar