Freescale-semiconductor M68HC08 Bedienungsanleitung PDF herunterladen (Seite 23)

Design Considerations

Switch Circuitry

Using the ASB520 MC68HC908QT2 Based Infrared Remote Control Reference PC Board DRM045

MOTOROLA Design Considerations 23

The spreadsheet in Table 5-1 gives the decimal values seen by the A/D, based

on which switch is depressed. Because the voltage from the switches is

ratiometric to V

, power supply variation will have no effect on A/D readings.

The ±6% values in Table 5-1 indicate worst case values, as the resistors used

in the design are ±5%. The software uses the minimum values from the table

to decode the switches.

Table 5-1. Switch Input A/D Values

Switch Ideal Value Minus 6% Plus 6%

No switch 255 239.7 255

Power 170.5 160.3 180.7

Play 127.7 120 153.3

Forward 79.9 75.1 84.7

Reverse 40.8 38.4 43.3

Pause 14.8 13.9 15.6

Stop 0 0 0

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Freescale-semiconductor M68HC08 Bedienungsanleitung Seite 23