INTERFACING
THE LDD-
N514RI-RA
DISPLAY
If you refer back to
the pinout in Figure 1,
you will see that the 10
pins are drawn in a
single row which is
typical for LED display
pinouts. However, the
neat pin arrangement in
the pinout diagram is
rarely reflected in
physical reality; most
LED displays have two
rows of pins, and the
segment order is rarely
sequential. The N514RA
is an exception; the
pinout diagram exactly
reflects the physical
arrangement of the pins.
The physical segment
ordering exactly matches
the pinout diagram. The
N514RA's 10 pins are
arranged in a single row
along the bottom edge
of the display. In
addition, the pins are all bent at an
angle which means that the N514RA
can be directly inserted into a
■ FIGURE 4. Stripboard layout for
N514RA experiments.
because we'll use that information
when we implement our multiplexed
LED display.
52 February 2013
■ FIGURE 5. The completed stripboard inserted into a breadboard.
breadboard (or a single header on a
stripboard — hint, hint), and the eight
data pins perfectly line up with the
eight port B pins on the 20M2
processor.
Of course, we can't simply insert
the N514RA in line with the port B
side of the 20M2 because we need
to include current-limiting resistors
between the port B pins and the
display's data pins. Also, the display's
two common cathode pins will
require additional circuitry before
they can be connected to the 20M2
pins. However, a simple stripboard
circuit can solve both these
problems, allowing us to insert the
N514RA on the port B side of the
20M2 so that we can experiment
with it.
The stripboard layout is
presented in Figure 4; a larger
version is available for downloading
at the article link. The stripboard's
wiring is fairly simple, so I haven't
included a schematic; just refer to
the layout in Figure 4 for the
following discussion.
The 10-pin female header near
the top edge of the stripboard is
where the N514RA will be inserted.
The reverse-mounted male headers
on the lower edge of the board are
inserted next to the port B side of
the 20M2, with the ground pin in
line with the 20M2's ground pin.
(See the photo in Figure 5.)
As you can see, we are still able
to access the 20M2's ground pin, as
well as its serial out pin which you
may remember can also be accessed
as the "pseudo" A.0 pin. (If not, see
the February 2012 Primer
installment.) Also, the N514RA's
eight segment pins line up perfectly
with the port B pins which will
simplify the software conversion of a
digit to the corresponding LED
segment pattern.
The two cutout areas on the
bottom corners of the stripboard
allow room for the insertion of
jumpers or components that we'll be
using to interface the display. We
won't be using the ground pin at all,
