The 4-digit 7-segment display is an extension of the 1-digit 7-segment display discussed in Chapter 5. As with the 1-digit 7-segment display, there are seven LED segments on the 4-digit display, labelled a, b, … g and P or DP. There are an additional four pins controlling the 4-digit displays. The pin layout on the 4-digit 7-segment display is illustrated in Figure 6-1 and the order of the digits from the left-hand side is 1, 2, 3, and 4. The 4-digit 7-segment display has a common cathode and a digit display is on when the digit pin state is LOW, which is equivalent to the common pin connected to ground for the 1-digit 7-segment display.