AN1740 Freescale Semiconductor / Motorola, AN1740 Datasheet - Page 9

• Manufacturer Part Number: AN1740
• Description: Applications Using the Analog Subsystem on MC68HC05JJ/JP Series Microcontrollers
• Manufacturer: Freescale Semiconductor / Motorola

AN1740
MOTOROLA
a lower priority than other IRQ sources by polling the CMP1 or CPF1 bits
in the IRQ subroutine. If CPF1 is set, the IRQ subroutine could branch
within the IRQ subroutine or cause the IRQ subroutine to be exited and,
therefore, allow an analog interrupt to occur. In either case, the
subroutine called should clear the CPF1 bit so that future detection is
possible.
Case 4 uses comparator 1 as a monitor, but also uses the digital inputs
on PB2 and PB3 as a crude threshold detector. In this case, the software
can determine whether the comparator is checking voltages above or
below the digital threshold of port B. The digital threshold is typically 40%
to 60% of the V
PB2 and PB3 pins are configured as inputs with their pulldowns
disabled.
Case 5 uses comparator 1 as a monitor, but it also uses the digital output
on PB4 to alter the trip point for the comparator. As shown in
the PB4 output buffer could shunt the external reference divider causing
the comparator to set when the parallel combination of R1 and R3 is
connected to V
and R3 is connected to V
will show that the shunting of the external reference divider can be done
by the OR combination of the PB4, TCMP, or CMP1 functions so that the
control can be based on software control, timer control, or direct
feedback from comparator 1. In this case, it is important that the PB2 and
PB3 pins are configured as inputs with their pulldowns disabled.
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DD
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and then reset when the parallel combination of R2
supply voltage. In this case, it is important that the
SS
. Careful review of the port B description also
Voltage Comparators
Application Note
Figure
3,
9