 |
Os motores de busca de Datasheet de Componentes eletrônicos |
|
|
Os motores de busca de Datasheet de Componentes eletrônicos |
|
HT86A36 Folha de dados(PDF) 34 Page - Holtek Semiconductor Inc |
|
||||||||||||||||||||||||||||||
HT86A36 Folha de dados(HTML) 34 Page - Holtek Semiconductor Inc |
|
|
34 / 68 page  HT86Axx/HT86ARxx Rev. 1.10 34 December 12, 2012 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. 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. 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. Reset Functions There are five ways in which a microcontroller reset can occur, through events occurring both internally and ex- ternally: · Power-on Reset 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. 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 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. 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. For applications that operate within an environment where more noise is present the Enhanced Reset Cir- cuit shown is recommended. 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. R E S V D D S S T T i m e - o u t I n t e r n a l R e s e t 0 . 9 V D D t R S T D Power-On Reset Timing Chart R E S 0 . 1 m F 1 0 0 k W V D D V S S 0 . 0 1 m F 1 0 k W Enhanced Reset Circuit R E S S S T T i m e - o u t I n t e r n a l R e s e t 0 . 9 V D D 0 . 4 V D D t R S T D RES Reset Timing Chart R E S V D D V S S 0 . 1 m F 1 0 0 k W Basic Reset Circuit |
Nº de peça semelhante - HT86A36_12 |
|
Descrição semelhante - HT86A36_12 |
|
|
Ligação URL |
| Privacy Policy |
| ALLDATASHEETPT.COM |
| ALLDATASHEET é útil para você? [ DONATE ] |
Sobre Alldatasheet | Publicidade | Contato conosco | Privacy Policy | roca de Link | Lista de Fabricantes All Rights Reserved©Alldatasheet.com |
| Russian : Alldatasheetru.com | Korean : Alldatasheet.co.kr | Spanish : Alldatasheet.es | French : Alldatasheet.fr | Italian : Alldatasheetit.com Portuguese : Alldatasheetpt.com | Polish : Alldatasheet.pl | Vietnamese : Alldatasheet.vn Indian : Alldatasheet.in | Mexican : Alldatasheet.com.mx | British : Alldatasheet.co.uk | New Zealand : Alldatasheet.co.nz |
|
Family Site : ic2ic.com |
icmetro.com |
Portuguese ▼
English
Chinese
German
Japanese
Russian
Korean
Spanish
French
Italian
Portuguese
Polish
Vietnamese
Indian
Mexican
British
New Zealand
