74 November 2013
Discovery’s low byte of GPIO pins. Again, I used its high
byte of GPIO pins as the slider’s binary display.
Screenshot 5 retains the slider configuration. However,
nothing has really changed logically. The Discovery’s high
byte of GPIO pins is now representing data on the low byte
of GPIO pins as a decimal progress bar value.
Does 74LS7447 mean anything to you? If it doesn’t, the
7447 was the only way to drive a seven-segment LED
display module back in the day.
I can still remember when I tossed the 7447 concept
and used a PIC and I/O multiplexing to drive a four-digit set
of seven-segment display modules. These days, there are
many “automated” ways to drive seven-segment LED-based
If you need to emulate a seven-segment LED module,
check out Screenshot 6. The upper eight bits of the
Discovery GPIO pins have now been configured as a seven-segment display. There is no correlation between the slider
value and the display LED value. The pair of 7s results from
the seven-segment LED’s 8, 9, and 10 being attached to the
slider’s bits 0, 1, and 2.
■ Screenshot 4. No code, no compiler, no counter IC, no
switches. Just an Analog Discovery creating an instant
binary UP/DOWN counter.
■ Screenshot 3. Now, this is the way to add switches and
LEDs to a project. The virtual switches and LEDs come in
handy when you need to feed a microcontroller input pin
or read a microcontroller's output pin state.
■ Screenshot 6. The pair of sevens is not by design. The
seven-segment LED's 8, 9, and 10 bits just happen to be
electrically tied to the slider's 0, 1, and 2 bits, respectively.
■ Screenshot 5. In this shot, a progress bar replaces the
LED display. The lower eight bits of the Analog Discovery
GPIO are configured as outputs (slider). The upper eight
bits are inputs.
■ Screenshot 8. Bits 0 through 7 are the basis for our
eight-bit binary counter. I also chose to show the
simulated analog value of the bus versus time.
■ Screenshot 7. Microcontroller? We don't need no stinkin'
microcontroller. We can manipulate the analog or digital
domains by simply fiddling with the Analog Discovery's