Inside the LCD assembly, the COMx and SEGy lines are arranged in a grid pattern. The COM lines are typically referred to as the back-plane of the LCD. This software solution implements a quadruplex back-plane, which means there are four COMx lines that are driven in sequence. To turn a particular segment on, the particular coordinate is activated by ensuring the associated COMx and SEGy lines are driven opposite of each other, and then alternated as shown in Figure 1-1. To keep a segment off, the appropriate SEGy line is driven in the same pattern as the COMx line that is currently being cycled through.

From an MCU perspective, the appropriate pins need to be driven high, low, or floating in a repeated pattern to display an image or message. An example of one LCD update cycle is shown in Figure 1-1. When a COMx line is active, it is first driven low for an update period, then high the following period. When inactive, the pin is set to floating and thus driven to VDD/2 via the external resistors described in Section 2. To turn a SEGy on, it is driven high, then low over two periods, and follows the same pattern as the COMx signal to keep it off.