AN1740 Freescale Semiconductor / Motorola, AN1740 Datasheet - Page 54

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

Application Note
54
NOTE:
The CPF2 flag bit may get set incorrectly when changing channels to an
input source voltage which is near V
conversion software should account for this case and clear out any
unwanted CPF2 flags before starting another conversion.
This fault is most likely to occur if the input voltage being converted is
within 50 mV of V
reduced if the comparator’s input voltage is positive as defined by
Figure
positive input offset voltage case, with a negative input offset voltage
case when the INV bit is set. But, the user should not depend on this
always being true, since input offset is a production variation. A software
check using the internal V
state of the INV bit to use to select the more desired positive offset case
discussed in
If it does occur, this fault can be detected by the same software check
for the maximum conversion time used to detect the infinite conversion
TOF/OCF
CPFR2
CMP2
CPF2
Freescale Semiconductor, Inc.
CHG
CONVERSION 1
V
V
For More Information On This Product,
N
P
7. Typical MC69HC05JJ/JP series MCUs tend to have the
Go to: www.freescale.com
Comparator Inversion
Figure 22. Disabled Conversion A/D Fault
V
SS
SS
. The effect of disabled conversion fault can be
SS
channel could be used to determine which
V
P
CHANNEL
CHANGE
= V
NEGATIVE OFFSET CASE
N
– V
SS
CHANGE
FALSE FLAG
on page 16.
IO
V
N
as shown in
+
–
+
CONVERSION 2
V
IO
MODE 2 OR MODE 3 ONLY
–
Figure
+
–
V
IO
IDEAL
COMPARATOR
22. A/D
MOTOROLA
AN1740
CMP2