參數(shù)資料
型號: HD4074449
廠商: Hitachi,Ltd.
英文描述: 4-bit HMCS400-Series microcomputer(4位單片微計算機)
中文描述: 4位HMCS400系列微機(4位單片微計算機)
文件頁數(shù): 57/123頁
文件大?。?/td> 726K
代理商: HD4074449
HD404449 Series
57
Timer A
Timer A Functions:
Timer A has the following functions.
Free-running timer
Clock time-base
The block diagram of timer A is shown in figure 40.
1/4
1/2
32.768-kHz
oscillator
System
clock
Prescaler W
(PSW)
Selector
Selector
Prescaler S (PSS)
S
I
Timer A interrupt
request flag
(IFTA)
Clock
Overflow
Timer
counter A
(TCA)
Timer mode
register A
(TMA)
3
2 f
1/2 tw
cyc
f
tw
cyc
PER
2
÷
4
÷
8
÷
3
÷
1
÷
5
÷
1
÷
2
÷
2
÷
8
÷
1
÷
3
÷
W
W
Figure 40 Timer A Block Diagram
Timer A Operations:
Free-running timer operation: The input clock for timer A is selected by timer mode register A (TMA:
$008).
Timer A is reset to $00 by MCU reset and incremented at each input clock. If an input clock is applied
to timer A after it has reached $FF, an overflow is generated, and timer A is reset to $00. The overflow
sets the timer A interrupt request flag (IFTA: $001, bit 2). Timer A continues to be incremented after
reset to $00, and therefore it generates regular interrupts every 256 clocks.
Clock time-base operation: Timer A is used as a clock time-base by setting bit 3 (TMA3) of timer
mode register A (TMA: $008) to 1. The prescaler W output is applied to timer A, and timer A
generates interrupts at the correct timing based on the 32.768-kHz crystal oscillation. In this case,
prescaler W and timer A can be reset to $00 by software.
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