Figure 5. The breadboard.
though they are labeled as such.
This is because the board has the ability to interrupt
anything the chip is doing in order to program it. This is
not a big problem since there are still 28 regular input/output lines. Once you reassign the inputs and outputs to
your preferred pins, those assignments will be displayed
on the graphic editor screen. The new designations are to
the left of all the input and output pins. If you do assign an
input or output to a pin that cannot be assigned, the compiler will tell you.
Once everything compiles, you need to breadboard
the circuit. Pin 1 is marked on the board. It is much like a
44-pin chip. The only power pins necessary are the ground
(Gnd) on pin 22 and the + 5 VDC (Vcc) on pin 23. Hook up
all the resistors and LEDs. Turn the power on and pulse
the trigger input to get the counter circuit to work.
If you look at my project picture (Figure 5) closely,
you will see that I used half of a double digit, seven-segment display scrounged from old equipment. You'll also
find the additional 7404 inverter chip I used to build the
switch debounce circuit. You will also see the gray programming cable. It is not necessary to have the cable
plugged in while the counter circuit is running, but it won't
affect it if you do leave it plugged in.
I took a little chance in doing this project. Based on
the sheer cool factor of having an FPGA in my next robotics project, I bought a board and spent time to learn how
to program it. There were a few minor snags but once I got
rolling, the job was easy.
I can hardly wait to try out the waveform functions.
Since I am more of a visual, schematic type of person, I'll
probably stick to the graphical editor but the hardware
description languages may be right up your alley. In a
future article, I plan to implement a bit of Rodney Brooks'
subsumption architecture within the FPGA and build a
small bot that can explore rooms, follow light, avoid obstacles ,and avoid falling down stairs. NV
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