mc68hc05x4dw Freescale Semiconductor, Inc, mc68hc05x4dw Datasheet - Page 117

• Manufacturer Part Number: mc68hc05x4dw
• Description: Xc68hc705x4 Microcontroller
• Manufacturer: Freescale Semiconductor, Inc

Input capture
function
Input capture
registers
9-ptimer
Address:
Address:
When using the timer overflow function and reading the free-running
counter at random times to measure an elapsed time, a problem may
occur whereby the timer overflow flag is unintentionally cleared if:
Reading the alternate counter register instead of the counter register will
avoid this potential problem.
‘Input capture’ is a technique whereby an external signal (connected to
the TCAP pin) is used to trigger a read of the free-running counter. In this
way it is possible to relate the timing of an external signal to the internal
counter value, and hence to elapsed time.
The two 8-bit registers that make up the 16-bit input capture register are
read-only, and are used to latch the value of the free-running counter
after the input capture edge detector senses a valid transition. The level
transition that triggers the counter transfer is defined by the input edge
Reset:
Reset:
1. the timer status register is read or written when TOF is set, and
2. the LSB of the free-running counter is read, but not for the purpose
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$0014
$0015
Bit 15
Bit 7
Figure 8. Input Capture High Register (ICH)
Figure 9. Input Capture Low Register (ICL)
16-Bit Programmable Timer
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14
6
13
5
12
4
Undefined
Undefined
11
3
16-Bit Programmable Timer
10
2
MC68HC05X4 Rev 1.0
Timer functions
9
1
Bit 8
Bit 0