The Microcontroller Idea Book - Jan Axelson's Lakeview Research

Chapter 8
Figure 8-3. A 7-segment display can show numbers from 0 to 9, plus hex
digits A-F. In a common-cathode LED display, all of the cathodes connect
together, while in a common-anode display, all of the anodes connect.
The displays come in two types: common-anode or common-cathode. In a common-anode
display, the anodes of each segment connect internally. To use the display, you connect the
anodes to a voltage source and turn on individual segments by grounding them through a
current-limiting resistor. A common-cathode display is the opposite: the cathodes connect
internally, so you ground the cathodes and apply voltages through current-limiting resistors
at the segments you want to light.
Deciphering pinouts
Unfortunately, there isn’t much standardization for pinouts of 7-segment displays. If you
don’t know the pinout for a display, you can find it by experimenting. You’ll need a 330-ohm
resistor and a 5-volt supply.
Sometimes you’ll find CC or CA stamped on the package to indicate common cathode or
common anode. If even this information is lacking, begin by connecting one lead of the
130 The Microcontroller Idea Book