参数资料
型号: MC68HC11F1CFN4
厂商: Freescale Semiconductor
文件页数: 119/158页
文件大小: 0K
描述: IC MCU 512 EEPROM 4MHZ 68-PLCC
标准包装: 18
系列: HC11
核心处理器: HC11
芯体尺寸: 8-位
速度: 4MHz
连通性: SCI,SPI
外围设备: POR,WDT
输入/输出数: 30
程序存储器类型: ROMless
EEPROM 大小: 512 x 8
RAM 容量: 1K x 8
电压 - 电源 (Vcc/Vdd): 4.75 V ~ 5.25 V
数据转换器: A/D 8x8b
振荡器型: 内部
工作温度: -40°C ~ 85°C
封装/外壳: 68-LCC(J 形引线)
包装: 管件
RESETS AND INTERRUPTS
TECHNICAL DATA
5-1
SECTION 5 RESETS AND INTERRUPTS
Resets and interrupt operations load the program counter with a vector that points to
a new location from which instructions are to be fetched. A reset causes the internal
control registers to be initialized to a known state. The program counter is loaded with
a known starting address and execution of instructions begins. An interrupt temporarily
suspends normal program execution while an interrupt service routine is being execut-
ed. After an interrupt has been serviced, the main program resumes as if there had
been no interruption.
5.1 Resets
There are four possible sources of reset. Power-on reset (POR) and external reset
share the normal reset vector. The computer operating properly (COP) reset and the
clock monitor reset each has its own vector.
5.1.1 Power-On Reset
A positive transition on VDD generates a power-on reset (POR), which is used only for
power-up conditions. POR cannot be used to detect drops in power supply voltages.
A 4064 tcyc (internal clock cycle) delay after the oscillator becomes active allows the
clock generator to stabilize. If RESET is at logical zero at the end of 4064 tcyc, the CPU
remains in the reset condition until RESET goes to logical one.
It is important to protect the MCU during power transitions. To protect data in EE-
PROM, M68HC11 systems need an external circuit that holds the RESET pin low
whenever VDD is below the minimum operating level. This external voltage level de-
tector, or other external reset circuits, are the usual source of reset in a system. The
POR circuit only initializes internal circuitry during cold starts. Refer to Figure 2–3.
5.1.2 External Reset (RESET)
The CPU distinguishes between internal and external reset conditions by sensing
whether the reset pin rises to a logic one in less than two E-clock cycles after an inter-
nal device releases reset. When a reset condition is sensed, the RESET pin is driven
low by an internal device for four E-clock cycles, then released. Two E-clock cycles
later it is sampled. If the pin is still held low, the CPU assumes that an external reset
has occurred. If the pin is high, it indicates that the reset was initiated internally by ei-
ther the COP system or the clock monitor. It is not advisable to connect an external
resistor capacitor (RC) power-up delay circuit to the reset pin of M68HC11 devices be-
cause the circuit charge time constant can cause the device to misinterpret the type of
reset that occurred.
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Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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