mc68hc05pl4b Freescale Semiconductor, Inc, mc68hc05pl4b Datasheet - Page 56

• Manufacturer Part Number: mc68hc05pl4b
• Description: Low-cost Single-chip Microcontroller
• Manufacturer: Freescale Semiconductor, Inc

GENERAL RELEASE SPECIFICATION
9.4
9-6
The result obtained by an input capture will be one count higher than the value of
the free-running timer counter preceding the external transition. This delay is
required for internal synchronization. Resolution is affected by the prescaler,
allowing the free-running timer counter to increment once every four internal clock
cycles (eight oscillator clock cycles).
Reading the ICRH inhibits further captures until the ICRL is also read. Reading
the ICRL after reading the timer status register (TSR) clears the ICF ag bit. does
not inhibit transfer of the free-running counter. There is no con ict betw een read-
ing the ICRL and transfers from the free-running timer counters. The input capture
registers always contain the free-running timer counter value which corresponds
to the most recent input capture.
To prevent interrupts from occurring between readings of the ICRH and ICRL, set
the I bit in the condition code register (CCR) before reading ICRH and clear the I
bit after reading ICRL.
OUTPUT COMPARE REGISTERS
The Output Compare function is a means of generating an output signal when the
16-bit timer counter reaches a selected value as shown in Figure 9-8. Software
writes the selected value into the output compare registers. On every fourth inter-
nal clock cycle (every eight oscillator clock cycle) the output compare circuitry
compares the value of the free-running timer counter to the value written in the
output compare registers. When a match occurs, the timer transfers the output
level (OLVL) from the timer control register (TCR) to the TCMP.
Software can use the output compare register to measure time periods, to gener-
ate timing delays, or to generate a pulse of speci c duration or a pulse train of
speci c frequency and duty cycle on the TCMP.
ICRH
$0014
ICRL
$0015
U = UNAFFECTED BY RESET
reset:
reset:
W
W
R ICRH7
R
ICRL7
BIT 7
U
U
Figure 9-7. Input Capture Registers (ICRH, ICRL)
Freescale Semiconductor, Inc.
For More Information On This Product,
ICRH6
ICRL6
BIT 6
16-BIT PROGRAMMABLE TIMER
U
U
Go to: www.freescale.com
ICRH5
ICRL5
BIT 5
April 30, 1998
U
U
NOTE
ICRH4
ICRL4
BIT 4
U
U
ICRH3
ICRL3
BIT 3
U
U
ICRH2
ICRL2
BIT 2
U
U
ICRH1
ICRL1
BIT 1
U
U
MC68HC05PL4
ICRH0
ICRL0
REV 2.0
BIT 0
U
U