It is important to be familiar with some of the different types of chipKIT™ connections. The connections that can be used for input and output on the board are referred to as pins. The pins are accessible via black “boxes,” known as headers, which protrude from the board. The header is where the wires will attach to the pins on the chipKIT board. There are many pins on chipKIT boards, but we are only going to consider a few in this page.
Figures 1 and 2 indicate the pins that are currently of interest to us on an Uno32 and a Max32, respectively. The “digital pins” are generally arranged in two parallel rows. These pins are identified by numbers that are printed on the chipKIT boards. For the Uno32, and for the digital pins at the top of the Max32, the numeric labels for the pins are not immediately adjacent to the pins. Instead, as shown in Figs. 1 and 2, the “upper” and “lower” labels correspond to the “upper” and “lower” pins. In Fig. 1, arrows are used to identify pin 33 and its label, as well as pin 3 and its label. In Fig. 2, arrows identify pin 77 and its label, as well as pin 3 and its label. In contrast to the pins at the top of the board, for the digital pins along the right side of the Max32, each label is adjacent to its corresponding pin (see Fig. 2).
Figures 1 and 2 also identify ground pins and source pins. Ground pins are always at a potential of 0V. The 5V pins and 3.3V pins, which are source pins, always maintain their respective positive voltages. Typically ground pins will be identified with the label “GND”. However, because of space constraints, the ground pin at the “top” of the Uno32 is merely labeled “G.” There is one other “labeling issue” that is worth noting. Although it is not shown on the labels in Fig. 2, as you will see if you look at a physical board, the labels associated with the top-left header on the Max32 had to be shifted slightly to the right. As a result, the labels for the five left-most pairs of pins are somewhat “scrunched” together and do not appear directly below their respective pins.
The digital pins can be configured either to read input or write output (essentially, digital pins are all pins that are labeled with a simple integer; analog pins are labeled with the letter “A” and an integer). When a digital pin is configured for output, the pin can be set to one of two states. The pin's state is set, using the appropriate programming statements, to either HIGH or LOW. When set to HIGH, a digital pin maintains a voltage of 3.3V. When set to LOW , a digital pin maintains a voltage of 0V.
As something of an aside, some of the digital pin numbers are underlined. These pins can be used to produce pulse width modulated (PWM) signals. We aren't currently interested in using this capability but will explore it later.