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4-MULTIPLEXED LCD WITH A STANDARD ST62

2 LCD DRIVING SOFTWARE LIBRARY

This library consists in one MAST6 source file, LCD_drv.st6, and its associated include file,

LCD_drv.inc

. It is targeted to a certain kind of LCD structure. Source code is provided to fa-

cilitate customisation to a particular LCD and application. The following section presents some

guidelines on how to use and customize the library.

The targeted LCD is organized into four classical 7-segment digits, plus four icons (e.g. a

colon at the middle), creating four “8-segment digits”. Each digit uses the four backplane pins

and two frontplane pins.

Figure 6. Connections for an 8-segment digit (example with a colon)

Typically, this kind of LCD is suited to 24-hour clock display. Therefore, the digits are called,

from left to right: “hours digit 1”, “hours digit 0”, “minutes digit 1”, “minutes digit 0”.

The first part of this section explains how to use the library provided the LCD is wired exactly

like the target is, and provided the MCU pin allocations are compatible with the rest of the ap-

plication. The second part gives more details on the data operations performed internally by

the driver, to be able to customise it if necessary. Finally, the third part gives an example of

how to manage timing resources to combine LCD requirements with the main tasks of the ap-

plication.

2.1 NON-CUSTOMISED USAGE

2.1.1 Allocation of I/O resources

All the MCU output pins generating the

S signals are located in the same I/O port, called “seg-

ments port”. A different I/O port, called “commons port” is used for the pins generating the

COM signals. The software driver has no effect on the other I/O pins, even if they are located

in one of those ports.

AM

PM

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