2 Configuration of the LCD Charge Pump

The LCD charge pump is enabled by setting LCDPEN of Configuration Word 1. Once the LCD charge pump has been enabled, it should be expected that it will generate VLCD3, thus providing power directly to the display. The LCD charge pump can be bypassed by clearing LCDPEN of Configuration Word 1, which would force it off and the LCD bias voltages would need to be derived using the other source options. For more information about using the LCD module without the charge pump enabled, please refer to the device data sheet. The LCD charge pump can be configured in a variety of different ways to satisfy specific LCD panel drive requirements, which will be discussed in the sections to follow.

Once enabled, the LCD charge voltage settings must be configured to meet the requirements of the display being used. The LCDVCON1 and LCDVCON2 registers contain several different configurations that pertain to the voltage and power options pertaining to the LCD module. The LCD voltage source is completely configurable by the user and should be programmed appropriately when the charge pump is enabled. The LCD voltage source is selected by programming the LCD Voltage Source Control bits (LCDVSRC<3:0>) of the LCDVCON2 register. Table 2-1 summarizes the various LCDVSRC<3:0> settings available. When using the LCD charge pump in an application, these bits should be programmed to ‘1001’, ‘0111’ or ‘0110’. Otherwise, the module will behave as if all sources are disabled. All other settings for this register are valid only when the charge pump has been bypassed (LCDPEN = 0).