MC68HC05B6_13 Datasheet, PDF (66/302 Pages) Freescale Semiconductor, Inc – Microcontrollers

The result obtained from an input capture will be one greater than the value of the free-running
counter on the rising edge of the internal bus clock preceding the external transition. This delay is
required for internal synchronization. Resolution is one count of the free-running counter, which is
four internal bus clock cycles. The free-running counter contents are transferred to the input
capture register 1 on each valid signal transition whether the input capture 1 flag (ICF1) is set or
clear. The input capture register 1 always contains the free-running counter value that
corresponds to the most recent input capture 1. After a read of the input capture 1 register MSB
($14), the counter transfer is inhibited until the LSB ($15) is also read. This characteristic causes
the time used in the input capture software routine and its interaction with the main program to
determine the minimum pulse period. A read of the input capture 1 register LSB ($15) does not
inhibit the free-running counter transfer since the two actions occur on opposite edges of the
internal bus clock.
5
Reset does not affect the contents of the input capture 1 register, except when exiting STOP mode
(see Section 5.6).
5.3.2 Input capture register 2 (ICR2)
Input capture high 2
Input capture low 2
Address bit 7
bit 6
bit 5
bit 4
bit 3
bit 2
bit 1
bit 0
State
on reset
$001C
Undefined
$001D
Undefined
The two 8-bit registers that make up the 16-bit input capture register 2 are read-only, and are used
to latch the value of the free-running counter after the input capture edge detector circuit 2 senses
a negative transition at pin TCAP2. When an input capture 2 occurs, the corresponding flag ICF2
in TSR is set. An interrupt can also accompany an input capture 2 provided the ICIE bit in TCR is
set.The 8 most significant bits are stored in the input capture 2 high register at $1C, the 8 least
significant bits in the input capture 2 low register at $1D.
The result obtained from an input capture will be one greater than the value of the free-running
counter on the rising edge of the internal bus clock preceding the external transition. This delay is
required for internal synchronization. Resolution is one count of the free-running counter, which is
four internal bus clock cycles. The free-running counter contents are transferred to the input
capture register 2 on each negative signal transition whether the input capture 2 flag (IC2F) is set
or clear. The input capture register 2 always contains the free-running counter value that
corresponds to the most recent input capture 2. After a read of the input capture register 2 MSB
($1C), the counter transfer is inhibited until the LSB ($1D) is also read. This characteristic causes
the time used in the input capture software routine and its interaction with the main program to
determine the minimum pulse period. A read of the input capture register 2 LSB ($1C) does not
inhibit the free-running counter transfer since the two actions occur on opposite edges of the
internal bus clock.
Reset does not affect the contents of the input capture 2 register, except when exiting STOP mode
(see Section 5.6).
Freescale
5-8
PROGRAMMABLE TIMER
MC68HC05B6
Rev. 4.1