; FIGURE 1. Schematic for the display.
11-15. The user interface and MC14489 interface are on
port B. This takes advantage of the available weak pull-ups
on this port for the input buttons; it
also reduces the parts count. The
16F819 has the option of using an
internal oscillator and internal
MCLR pull-up resistor which can
free-up additional pins on port A.
In this design, I have MCLR pulled
up externally so the PIC can be
easily reset. I am using the PIC’s
internal oscillator to free-up I/O
pins RA6 and RA7 for future use,
and I set the oscillator frequency to
4 MHz by configuring the
OSCCON register in the code.
Several other I/O pins on port A
and port B are available to add
other functions, sensors, etc., to the
circuit, or to interface the display
module to external systems.
When you program your PIC,
you will need to select the
“INTIO2” oscillator configuration option to enable the
internal oscillator. Note that not all programmer software
; FIGURE 2. Front and back of the prototype display;
note the rat's nest of point-to-point wiring.
July 2012 37