> Van: John Esposito <John_Esposito@DADEBEHRING.COM>
> Aan: PICLIST@MITVMA.MIT.EDU
> Onderwerp: Remote keypads - which PIC?
> Datum: donderdag 13 mei 1999 17:23
>
> Hello all.

Hello John,

> I am trying to implement several remote keypads with one central master,
> very similar to a home security system.  Each keypad uses a 4x4 matrix
> keypad, a 16x2 backlit LCD, 3 diodes, a piezo buzzer, and 2-wire serial
> communications with the master.
>
> I have been gradually incorporating each of these into a PIC16C84, but a
> rapidly running out of I/O (only 13) pins even with the use of shift
> registers and a software SPI.  I eventually want to migrate this to a
> cheaper chip, perhaps an 18-pin PIC16C5x or PIC16C62.

My first thought was how to combine all those devices.  With some
restrictions I came to the following, using _all_ pins.  One LED could be
added though :-)

B0-3 A0  LCD in 4-bit mode, Write only. (B0-3 := Data, A0 := Enable)
B0-3 A1  Led's (B0-3 := Anode's, A1 := common Kathode)
B0-7       Keyboard (B0-3 := Out, B4-7 In -> wake-up on change enabled)
A2          Buzzer (taking you use a Piezo, so multiplexing it is not
possible)
A3-A4     I2C (A3 := Clock, A4 := Data -> OC output & wake-up on change)

By using B4-7 as inputs from the Keyboard a Wake-up function (on key-press)
could be implemented.  Using A4 as I2C-data input serves two functions:
One: it's Open-collector (required when using I2C) and a
Interrupt-possibility when detecting data-change.

Greetz,
  Rudy Wieser