Murphy, Patrick (AZ76) wrote:

> The project I have in mind is a device with two 2-digit readouts (four
> 7-segment LEDs), and two sets of 2 pushbutton inputs.

> At first pass, it seems to me that I do not have enough I/O lines
> available on the 16F84 to drive four 7-segment LEDs.

  The nub of my previous postings on this subject, describing hardware
*and* software, was that using nine PIC lines you should be able to
readily multiplex eight (or was that nine?) 7-segment displays including
decimals; or eight PIC lines to drive eight displays without decimals.
Multiplex division is by digit, i.e., one in four for a four digit
display.

  Hardware requirement is: common anode displays, eight resistors, one
NPN driver transistor per display.  The strobe lines can be used at the
same time to multiplex the keyboard; you would require one keyboard
data line.  This could possibly be substituted for one of the already
used I/O lines not required to strobe a digit; i.e., less than 8 display
digits used.

  Look in the archives for: "Re: loads of flashing LEDs" over the period
approximately 98/07/22 to 98/07/30 for an explanation of the technique.

  I really must FAQ it on my site!
--
  Cheers,
        Paul B.