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HT46R01 参数 Datasheet PDF下载

HT46R01图片预览
型号: HT46R01
PDF下载: 下载PDF文件 查看货源
内容描述: 10引脚MSOP A / D型8位OTP MCU [10-Pin MSOP A/D Type 8-Bit OTP MCU]
分类和应用:
文件页数/大小: 60 页 / 482 K
品牌: HOLTEK [ HOLTEK SEMICONDUCTOR INC ]
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HT46R01/HT46R02/HT46R03  
Reset and Initialisation  
A reset function is a fundamental part of any  
microcontroller ensuring that the device can be set to  
some predetermined condition irrespective of outside  
parameters. The most important reset condition is after  
power is first applied to the microcontroller. In this case,  
internal circuitry will ensure that the microcontroller, af-  
ter a short delay, will be in a well defined state and ready  
to execute the first program instruction. After this  
power-on reset, certain important internal registers will  
be set to defined states before the program com-  
mences. One of these registers is the Program Counter,  
which will be reset to zero forcing the microcontroller to  
begin program execution from the lowest Program  
Memory address.  
inhibited. After the RES line reaches a certain voltage  
value, the reset delay time tRSTD is invoked to provide  
an extra delay time after which the microcontroller will  
begin normal operation. The abbreviation SST in the  
figures stands for System Start-up Timer.  
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Power-On Reset Timing Chart  
For most applications a resistor connected between  
VDD and the RES pin and a capacitor connected be-  
tween VSS and the RES pin will provide a suitable ex-  
ternal reset circuit. Any wiring connected to the RES  
pin should be kept as short as possible to minimise  
any stray noise interference.  
In addition to the power-on reset, situations may arise  
where it is necessary to forcefully apply a reset condition  
when the microcontroller is running. One example of this  
is where after power has been applied and the  
microcontroller is already running, the RES line is force-  
fully pulled low. In such a case, known as a normal oper-  
ation reset, some of the microcontroller registers remain  
unchanged allowing the microcontroller to proceed with  
normal operation after the reset line is allowed to return  
high. Another type of reset is when the Watchdog Timer  
overflows and resets the microcontroller. All types of re-  
set operations result in different register conditions be-  
ing setup.  
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Basic Reset Circuit  
For applications that operate within an environment  
where more noise is present the Enhanced Reset Cir-  
cuit shown is recommended.  
Another reset exists in the form of a Low Voltage Reset,  
LVR, where a full reset, similar to the RES reset is imple-  
mented in situations where the power supply voltage  
falls below a certain threshold.  
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Reset Functions  
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There are five ways in which a microcontroller reset can  
occur, through events occurring both internally and ex-  
ternally:  
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Power-on Reset  
Enhanced Reset Circuit  
The most fundamental and unavoidable reset is the  
one that occurs after power is first applied to the  
microcontroller. As well as ensuring that the Program  
Memory begins execution from the first memory ad-  
dress, a power-on reset also ensures that certain  
other registers are preset to known conditions. All the  
I/O port and port control registers will power up in a  
high condition ensuring that all pins will be first set to  
inputs.  
More information regarding external reset circuits is  
located in Application Note HA0075E on the Holtek  
website.  
·
RES Pin Reset  
This type of reset occurs when the microcontroller is  
already running and the RES pin is forcefully pulled  
low by external hardware such as an external switch.  
In this case as in the case of other reset, the Program  
Counter will reset to zero and program execution initi-  
ated from this point.  
Although the microcontroller has an internal RC reset  
function, if the VDD power supply rise time is not fast  
enough or does not stabilise quickly at power-on, the  
internal reset function may be incapable of providing  
proper reset operation. For this reason it is recom-  
mended that an external RC network is connected to  
the RES pin, whose additional time delay will ensure  
that the RES pin remains low for an extended period  
to allow the power supply to stabilise. During this time  
delay, normal operation of the microcontroller will be  
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RES Reset Timing Chart  
September 21, 2007  
Rev. 1.00  
36  
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