AN1740 Freescale Semiconductor / Motorola, AN1740 Datasheet - Page 43

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

16-Bit Timer
Input Capture
AN1740
MOTOROLA
The 16-bit timer is the same one found on some other members of the
MC68HC05 Family of MCUs. In the JJ/JP series, it has an additional
purpose in providing the A/D timing in mode 2 or mode 3. It may be
difficult to use the input capture and output compare timing functions for
external events while still using them for the A/D conversions, but careful
planning of the A/D sampling and conversion times will provide more
capability for activities to be done in parallel.
When using the 16-bit timer for an A/D mode 2 or mode 3 conversions,
the ICIE and IEDG bits in the TCR must be set in addition to the ICEN
bit in the ACR. This is because the input capture function must be
enabled and set up to trigger on the rising output of comparator 2. If one
or more of these bits is left cleared, A/D conversions will not take place.
The ICF, OCF, and TOF timer flags interact to start and stop the current
source driving PB0. Under this control, the ICF has priority over both the
OCF and TOF. Further, the latched static flag, CPF2, of comparator 2 is
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Figure 19. Typical Input Pulldown Current
1
2
INPUT VOLTAGE – VOLTS
V
DD
= 3.0 V
3
V
DD
= 5.0 V
4
Support Circuitry
Application Note
T
A
= 25 C
5
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