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Conectare pin reset

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Resetul dupa cum apare in prospect are intern un pull-up de 45k , asa in medie .

Cu toate astea , ca inca nu am priceput de ce , mai apare recomandarea sa se mai puna ceva in paralel afara . 

Eu nu am inteles logica ; astfel:

-cind poate functiona numai cu cel intern 

-la programare ISP ce valoare are nevoie ? merge numai cu cel intern ?

-sau poate ca s-a prevazut resetul intern doar pentru functionare si pentru regimul de programare in programator sa existe valoarea de paralel ?

In concluzie :

-asa , uzual trebuie sau nu ceva adaugat ?

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In mod uzual se conecteaza o rezistenta cu valaorea intre 4k7 si 10k intre pinul Reset si Vcc.

Daca vrei sa folosesti functia de reset intern atunci nu vei mai putea folosi programatorul serial pentru (re)programare.

De ce nu itesti tu bine foaia de catalog a microcontroller-ului?

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Am citit , dar nu am inteles . Nici acum nu prea sint lamurit . Am inteles cam asa . 

-ca daca exista reset extern aciv , este obligatoriu sa punem o rezistenta de pull-up de la reset .

-daca dezactivam reset extern , pinul se va transforma in o simpla intrare care are intern disponibil de folosit un pull-up . In acesta situatie , evident ca nu mai putem folosi programarea seriala.

 

Corect ?

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Nu este obligatorie, cel putin nu la programare, dar daca nu se pune acea rezistenta intre resest si + atunci la o simpla atingere cu degetul a pinului Mc-ul se reseteaza  astfel pun o rezistenta de 10k si astfel pot programa direct in montaj fara a fi nevoit sa scot rezistenta pentru aceasta, am preferat sa rezerv pinul reset strict pentru programare insa daca se doreste totusi folosirea sa ca I/O atunci nu se mai pune acea rezistenta dar nici Mc-ul nu-l vei mai putea reprograma decit daca-l deblochezi, cu un alt montaj....

Edited by nickrvl

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Aha , deci intern ar exista o rezistenta de pull-up . Cea exterioara , ar veni in paralel cu cea interioara , si astfel ii coboara valorea si implicit sensibilitatea . Am inteles .

Dar daca punem o astfel de rezistenta , in exterior va creste consumul global al mcu ?

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Eu sint convins ca nu, cel putin nu vad ce ar "activa" pentru ai creste consumul, chiar daca prin absurd aplicam 5v direct pe rezistenta (10k) fa tu calculul ce curent implica....

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Va rog sa cititi ceea ce spune Atmel:

 

"Connection of RESET Pin on AVRsThe RESET pin on the AVR is active LOW, and setting the pin LOW externally will thus result in a reset of theAVR. The RESET has two purposes:1. To release all lines by tri-stating all pins (except XTAL pins), initialize all I/O registers and set programcounter to zero.2. To enter programming mode (for some parts also the PEN line is used to enter programming mode).Furthermore it is possible to enter high-voltage/parallel programming mode by drawing the RESET pin“very” high, where very high means 11.5V – 12.5V (refer to the datasheet of the device for moreinformation).The reset line has an internal pull-up resistor, but if the environment is noisy it can be insufficient and reset cantherefore occur sporadically. Refer to datasheet for value of pull-up resistor on specific devices.Connecting the RESET so that it is possible to enter both high-voltage programming and ordinary low level resetcan be achieved by applying a pull-up resistor to the RESET line. This pull-up resistor makes sure that resetdoes not go low unintended. The pull-up resistor can in theory be of any size, but if the Atmel AVR should beprogrammed from e.g. STK®500/AVRISP the pull-up should not be so strong that the programmer cannotactivate RESET by draw the RESET line low. The recommended pull-up resistor is 4.7kΩ or larger when usingSTK500 for programming. For DebugWIRE to function properly, the pull-up must not be smaller than 10kΩ.To protect the RESET line further from noise, it is an advantage to connect a capacitor from the RESET pin toground. This is not directly required since the AVR internally have a low-pass filter to eliminate spikes and noisethat could cause reset. Applying an extra capacitor is thus an additional protection. However, note that thiscapacitor cannot be present if DebugWIRE or PDI is used.If not using High Voltage Programming it is recommended to add an ESD protecting diode from RESET to Vcc,since this is not internally provided due to High Voltage Programming. Alternatively, or in addition, a Zener diodecan be used to limit the RESET voltage relative to GND. The Zener diode is highly recommended in noisyenvironments. The components should be located physically close to the RESET pin of the AVR. Figure 2-1shows the recommended circuit on the RESET line."

 

@nickrvl: rezistenta aia este obligatorie cand nu dezactivezi pinul RESET (in scopul folosirii lui ca port I/O obisnuit). In caz contrar te vei intreba de ce montajul functioneaza cand este conectat la programator si nu mai functioneaza cand conectorul programatorului este decuplat de la montaj.

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...................

@nickrvl: rezistenta aia este obligatorie cand nu dezactivezi pinul RESET (in scopul folosirii lui ca port I/O obisnuit). In caz contrar te vei intreba de ce montajul functioneaza cand este conectat la programator si nu mai functioneaza cand conectorul programatorului este decuplat de la montaj.

Pai, eu nu am intrebat nimic, stiu ca trebuie..........

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