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MC68331CFC16 参数 Datasheet PDF下载

MC68331CFC16图片预览
型号: MC68331CFC16
PDF下载: 下载PDF文件 查看货源
内容描述: 用户手册 [User’s Manual]
分类和应用: 微控制器和处理器外围集成电路时钟
文件页数/大小: 254 页 / 1319 K
品牌: MOTOROLA [ MOTOROLA ]
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PITR  
SWP  
PTP  
FREEZE  
PITCLK  
8-BIT MODULUS  
COUNTER  
PIT  
INTERRUPT  
÷ 4  
CLOCK  
MUX  
PRECLK  
CLOCK  
DISABLE  
9
EXTAL  
PRESCALER (2 )  
RESET  
SWCLK  
LPSTOP  
SWT1  
SWT0  
SWE  
15 STAGE  
DIVIDER CHAIN (2  
15  
)
9
2
11  
2
13  
2
15  
2
PIT BLOCK  
Figure 4-3 Periodic Interrupt Timer and Software Watchdog Timer  
4.2.11 Periodic Interrupt Timer  
4
The periodic interrupt timer allows the generation of interrupts of specific priority at pre-  
determined intervals. This capability is often used to schedule control system tasks  
that must be performed within time constraints. The timer consists of a prescaler, a  
modulus counter, and registers that determine interrupt timing, priority and vector as-  
signment. Refer to SECTION 5 CENTRAL PROCESSING UNIT for further information  
about interrupt exception processing.  
The periodic interrupt modulus counter is clocked by a signal derived from the buffered  
crystal oscillator (EXTAL) input pin unless an external frequency source is used. The  
value of the periodic timer prescaler (PTP) bit in the periodic interrupt timer register  
(PITR) determines system clock prescaling for the watchdog timer. One of two op-  
tions, either no prescaling, or prescaling by a factor of 512, can be selected. The value  
of PTP is affected by the state of the MODCLK pin during reset, as shown in Table 4-  
5. System software can change PTP value.  
Table 4-5 MODCLK Pin and PTP Bit at Reset  
MODCLK  
PTP  
0 (External Clock)  
1 (Internal Clock)  
1 (÷ 512)  
0 (÷ 1)  
Either clock signal (EXTAL or EXTAL ÷ 512) is divided by four before driving the mod-  
ulus counter (PITCLK). The modulus counter is initialized by writing a value to the pe-  
riodic timer modulus timer modulus (PITM) field in the PITR. A zero value turns off the  
periodic timer. When the modulus counter value reaches zero, an interrupt is generat-  
ed. The modulus counter is then reloaded with the value in PITM and counting repeats.  
If a new value is written to PITR, it is loaded into the modulus counter when the current  
count is completed.  
MC68331  
SYSTEM INTEGRATION MODULE  
MOTOROLA  
4-7  
USER’S MANUAL