AN1048

Example of a quadruplex LCD with ST72F321B

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Example of a quadruplex LCD with ST72F321B

The following example describes a drive for a quadruplex mode (4COM) LCD using the

ST72F321B (TQFP64 pin package 10 x 10). Refer to Figure 8. The only external

components needed for driving the LCD are eight resistors. The resistor value of 56K is

used to reduce the DC voltage on the LCD(~7.5 mV). This value can be further decreased

to get the better DC voltage on the LCD but this will result in an increase of the current

consumption. One I/O port per segment and one I/O port for each COM line are needed to

drive the LCD. For example: To drive a quadruplex LCD that has 128 segments (with 32

segment lines and 4 COM lines) requires only a total of 36 I/O ports.

In the example program, the Port PA0-A5, PB0-B7, PD0-D7, PF7-F0, PE7-E6 pins are

connected to the 32 segment lines and are used to generate the segment signals. Ports

PC3...PC0 are connected to the 4 COM lines and used to generate the COM signals. The

LCD driver consists of two initialization routines (port init, timer init) and a TimerA interrupt

routine “timer_rt”. To activate the LCD, these two initialization routines have to be called.

After these routines are called, the ST7 gets the timer Output Compare 1 & Output Compare

2 interrupts.