Hello,

What is the best way to sense a push button press?  I am multiplexing the
PORTB data lines as a data bus and using PORTA as chip select as shown
to me by Steve Smith.  Will the below circuit work?

An HC74 D Flip-Flop is used to capture a push button press since inputs
will only be scanned briefly and I don't want to miss the press.

The inputs are selected by selecting RD1 and storing to a register.
If PB0 reads as set then I know that the button was pressed.  I then
reset the F/F by selecting WR1 and tickling PB7.

Is there a better way to achieve this???  I need to multiplex the pins
since there are many inputs and outputs (LCD display, ISD voice chip etc)

All comments are appreciated (but go easy on me -- I am also a newbie!)

Thanks in advance!

-Randie Ohtsji
rohtsji@glenayre.com

PS  I hope my crude schematic shows what I am doing.



                                                Vcc
   +--------------To PIC16F84                    |
   |                 PORTB0-7                    /
   |                                             \
   |                                             /
   |                                             \
   |                                             /      | N.O. Push button
   |                                             |     _|_
   |               __________                    |
   |              |          |                   +-----0 0-------Gnd
   |     8        |        Q0|----               |
   +----/---------| HC373  Q1|----               |
   |              | __     Q2|----           ____0___
   |      GND-----0 OE     Q3|----          |    _   |
   |              |        Q4|----     +----|D   S  Q|------------+
   |              |        Q5|----     |    |  HC74  |            |
   |              |        Q6|----     |    |       _|            |
   |       WR1----|LAT     Q7|-------------->CLK _  Q|-----+      |
   |              |__________|         |    |____R___|     |      |
   |                                   |         0         |      |
   |                                   |         |         |      |
   |                                   +-------------------+      |
   |                                             |                |
   |               __________                    \                |
   |              |          |                   /                |
   |              |        A0|------------------ \ ---------------+
   |      8       |  HC244 A1|                   /
   +-----/--------|        A2|                   \
                  | ___    A3|                   /
        RD1--+----0 OE1    A4|                   |
             |    | ___    A5|                   Vcc
             +----0 OE2    A6|
                  |        A7|
                  |__________|

                   __________
                  | __       |
          WR1-----0 Y0     A0|-------    \
                  | __HC138  |            \
          RD1-----0 Y1     A1|-------      \ To PIC16F84
                  | __       |             / PORTA0-2
                  0 Y2     A2|-------     /
                  | __       |
                  0 Y3    CS1|-----/\/\/\----Vcc
                  | __    ___|
                  0 Y4    CS20---+------GND
                  | __    ___|   |
                  0 Y5    CS30---+
                  | __       |
                  0 Y6       |
                  | __       |
                  0 Y7       |
                  |__________|