MC68HC05X4 Datasheet, PDF (117/156 Pages) Motorola, Inc – HCMOS Microcontroller Unit

Input capture
function
Input capture
registers
9-ptimer
MOTOROLA
Freescale Semiconductor, Inc.
16-Bit Programmable Timer
Timer functions
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:
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
of servicing the flag.
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.
Address: $0014
Bit 15
14
13
12
11
10
9
Bit 8
Reset:
Undefined
Figure 8. Input Capture High Register (ICH)
Address: $0015
Bit 7
6
5
4
3
2
1
Bit 0
Reset:
Undefined
Figure 9. Input Capture Low Register (ICL)
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
16-Bit Programmable Timer
For More Information On This Product,
Go to: www.freescale.com
MC68HC05X4 Rev 1.0
117