Motorola USB08 3.9 LED Control with U08LED.H, 3.10 Software ADC Module U08ADC.C

Designer Reference Manual USB08 Evaluation Board

52 Software Module Descriptions MOTOROLA

Software Module Descriptio ns

NOTE: It has to be pointed out for com pleteness, that with the KBI module o f the

MC68HC908JB8 not only single keys but also extensive key fields in

matrix arrangement can be easily scanned.

3.9 LED Control with U08LED.H

Controlling the three light-emitting diodes (LED) attached to port D is

easy. For initialization, the data direction of the used port pins PTD[0 ..2]

has to be switched to an output state. The initialization as well as the

switching of the LEDs is performed via four macros. Therefo re, a header

file is enough for the realization of these functions. A special C module

is not required in this case.

The LEDs are addressed, beginning with a 1. The switching on of the

first LED (at PTD[0]) takes place, for example, by means of:

onLED(1);

3.10 Software ADC Module U08ADC.C

Although the MC68HC908JB8 does not have an integrated ADC, it is

nevertheless possible to measure analog values (and in particular

resistance values) in a simple way. For this purpose, a n RC combinat ion

is attached to a conventional digital port pin and the load time of the

capacitor is measured. The working principle is shown in Figure 3-2.

Figure 3-2. Measurement of Resistor Values Using a Digital Input

VCC

GND