course, is provided by the braided shield in the cable.
So, the tip connects to port line B.0 (pin 6), while the
ring goes to B.1 (pin 7) of the PIC16F88. Observe how
uncomplicated everything is. This is a direct connection
and no additional circuitry is called for!
Just so we can see what’s going on, let’s also attach
an LCD to the PIC as shown in the schematic. There’s
nothing new or unusual here, as this is the typical way to
connect an LCD for four-bit operation. You’ll note R2
which is the current-limiting resistor for the LED backlight
of the LCD. Just use whatever value is specified in your
Well, that was pretty painless. If you’ve got it all
breadboarded as shown in Figure 2, let’s see how to make
the bits flow unabated between the PIC and the TI- 83 Plus
Low Level Communication
Since only two wires are used to communicate
between the devices, you might guess there’s some fancy
footwork involved ... you’d be right. The data transmission
is bidirectional; the PIC sends a computation to the
calculator, which then returns the result amidst a flurry
of handshaking. Plus, everything must happen
asynchronously. That’s a lot to ask of two wires, but it all
works out quite handily. In what follows, we’ll call these
lines Data0 and Data1.