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Rev. 1.21
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HT66F488/HT66F489
A/D Flash MCU with EEPROM
HT66F488/HT66F489
A/D Flash MCU with EEPROM
Capture Input Mode
To select this mode bits PTnM1 and PTnM0 in the PTMnC1 register should be set to 01 respectively.
This mode enables external signals to capture and store the present value of the internal counter
and can therefore be used for applications such as pulse width measurements. The external signal is
supplied on the PTPn or PTCKn pin, selected by the PTnCKS bit in the PTMnC1 register. The input
pin active edge can be a rising edge, a falling edge or both rising and falling edges; the active edge
transition type is selected using the PTnIO1 and PTnIO0 bits in the PTMnC1 register. The counter
is started when the PTnON bit changes from low to high which is initiated using the application
program.
When the required edge transition appears on the PTPn or PTCKn pin the present value in the
counter will be latched into the CCRA registers and a TM interrupt generated. Irrespective of what
events occur on the PTPn or PTCKn pin the counter will continue to free run until the PTnON
bit changes from high to low. When a CCRP compare match occurs the counter will reset back
to zero; in this way the CCRP value can be used to control the maximum counter value. When a
CCRP compare match occurs from Comparator P, a TM interrupt will also be generated. Counting
the number of overflow interrupt signals from the CCRP can be a useful method in measuring long
pulse widths. The PTnIO1 and PTnIO0 bits can select the active trigger edge on the PTPn or PTCKn
pin to be a rising edge, falling edge or both edge types. If the PTnIO1 and PTnIO0 bits are both set
high, then no capture operation will take place irrespective of what happens on the PTPn or PTCKn
pin, however it must be noted that the counter will continue to run.
As the PTPn pin is pin or PTCKn pin shared with other functions, care must be taken if the PTMn
is in the Input Capture Mode. This is because if the pin is setup as an output, then any transitions on
this pin may cause an input capture operation to be executed. The PTnCCLR, PTnOC and PTnPOL
bits are not used in this Mode.