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EMBEDDED MULTITASKING

The Easy Way
by Charles Kosina

Start ý An Example ý State Machine Control ý Keyboard Scanning ý Receive Serial Data ý LCD Module ý Transmit Data ý Debugging Techniques ý Other Options ý Sources and PDF

LCD MODULE

All the gathered data is displayed on a 20 ý 2 LCD module. Figure 3 shows the state machine for this task, where state 0 monitors flags from the other tasks. As soon as one is set, the appropriate field on the LCD is updated. Incoming data from the RS-232 port is displayed on the first line, and keyed-in data is displayed on the second line.

Figure 3ýHere are the LCD module state machine test flags from the keyboard and RS-232 state machines. The appropriate field is updated on the module when a flag is detected.

I have to confess to breaking one of my own rules. In the drivers for the LCD, I have delays of up to several milliseconds, which (though timer-generated) are totally within one of the states. This doesnýt create any problems in this example, but for complex and time-critical applications, the display drivers should be rewritten to avoid this.

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