參數(shù)資料
型號: MC68HC05JB4DWR2
廠商: MOTOROLA INC
元件分類: 微控制器/微處理器
英文描述: 8-BIT, MROM, 3 MHz, MICROCONTROLLER, PDSO28
封裝: SOIC-28
文件頁數(shù): 93/134頁
文件大?。?/td> 1305K
代理商: MC68HC05JB4DWR2
February 24, 1999
GENERAL RELEASE SPECIFICATION
MC68HC05JB4
16-BIT TIMER
MOTOROLA
REV 2
9-5
NOTE
To prevent interrupts from occurring between readings of the ACRH and ACRL,
set the I bit in the condition code register (CCR) before reading ACRH and clear
the I bit after reading ACRL.
9.3
INPUT CAPTURE REGISTERS
The input capture function is a technique whereby an external signal (connected
to PB0/ICAP1 pin) is used to trigger the 16-bit timer counter. In this way it is possi-
ble to relate the timing of an external signal to the internal counter value, and
hence to elapsed time.
When the input capture circuitry detects an active edge on the ICAP1 pin, it
latches the contents of the free-running timer counter registers into the input cap-
ture registers as shown in Figure 9-6.
Latching values into the input capture registers at successive edges of the same
polarity measures the period of the selected input signal. Latching the counter val-
ues at successive edges of opposite polarity measures the pulse width of the sig-
nal.
Figure 9-6. Timer Input Capture Block Diagram
The input capture registers are made up of two 8-bit read-only registers (ICRH,
ICRL) as shown in Figure 9-7. The input capture edge detector contains a Schmitt
trigger to improve noise immunity. The edge that triggers the counter transfer is
dened by the input edge bit (IEDG) in the TCR. Reset does not affect the con-
tents of the input capture registers.
ICIE
ICRH ($0014)
16-BIT COUNTER
÷ 4
INTERNAL
(fOSC ÷ 2)
TIMER CONTROL REG.
TIMER
REQUEST
INPUT CAPTURE (ICF)
RESET
CLOCK
INTERRUPT
ICRL ($0015)
ICF
TIMER STATUS REG.
$0012
$0013
INTERNAL
($FFFC)
DATA
READ
ICRH
READ
ICRL
LATCH
BUS
IEDG
EDGE
SELECT
& DETECT
LOGIC
IEDG
PB0/ICAP1
INTERNAL
DATA
BUS
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