Post by thread:[pic] : mclr versus cycling the power

alright, you guys got me interested in building a hobby board... in my solderless breadboard circuits, I just have a 4.7k resistor from mclr to +5vdc I think the data sheet tells you to take mclr to ground, to reset the pic, true? if so, what is the difference between doing this and recycling the power? or is a reset exactly the same as powering off then on? second. can you use a reset, to get bootloader programs to load up?? (I have always been using a power reset?) thanks for any lumination... so far, a printed circuit hobby board for me would be a big improvement if it just had the pic and the power supply, so that's what I'm doing. a 7805 with a capacitor, a power led and resistor and a switch. and the pic with the registers going to a socket where I can jam a solderless breadboard connector wire...and I use rb6 and rb7 thru resisters for programming via bootloader and rs232 feedback -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

> if so, what is the difference between doing this and > recycling the power? or > is a reset exactly the same as powering off then on? Power cycling is the more thorough reset. Some components (LCDs for instance) don't even have a real (external) reset pin. I almost always use a 7805 regulator and, I often use a switch that shorts the 5 Volt as reset. For programming some newer PICs require MCLR rise to Vpp *before* +5 is applied. Wouter van Ooijen -- ------------------------------------------- Van Ooijen Technische Informatica: http://www.voti.nl consultancy, development, PICmicro products -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

on the bootloader I use melabs loader and it will work with either. regards Victor ----- Original Message ----- From: "rad0" <spam_OUTrad0TakeThisOuTATTBI.COM> To: <.....PICLISTKILLspam@spam@MITVMA.MIT.EDU> Sent: Sunday, January 19, 2003 10:51 AM Subject: [pic] : mclr versus cycling the power > alright, you guys got me interested in building a hobby board... > > in my solderless breadboard circuits, I just have a 4.7k resistor from mclr > to +5vdc > > I think the data sheet tells you to take mclr to ground, to reset the pic, > true? > > if so, what is the difference between doing this and recycling the power? or {Quote hidden}> is a reset exactly the same as powering off then on? > > > second. can you use a reset, to get bootloader programs to load up?? > (I have always been using a power reset?) > > thanks for any lumination... > > > so far, a printed circuit hobby board for me would be a big > improvement if it just had the pic and the power supply, so that's > what I'm doing. a 7805 with a capacitor, a power led and resistor and a > switch. > and the pic with the registers going to a socket where I can jam a > solderless > breadboard connector wire...and I use rb6 and rb7 thru resisters for > programming > via bootloader and rs232 feedback > > -- > http://www.piclist.com hint: The PICList is archived three different > ways. See http://www.piclist.com/#archives for details. > -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

Dale, I think there is still a problem with the list reply address. I replied to the MCLR question and got the response below from the list server. I'm guessing that the original poster set his REPLY-TO address and the list server substituted the list server command address instead of the list distribution address. {Original Message removed}

I don't know about bootloaders, but there are status bits that are set on reset, and using them you can tell what kind of reset you've just experienced. In addition, I think some registers might have different values depending on POR or MCLR. Josh -- A common mistake that people make when trying to design something completely foolproof is to underestimate the ingenuity of complete fools. -Douglas Adams rad0 wrote: > I think the data sheet tells you to take mclr to ground, to reset the pic, > true? > > if so, what is the difference between doing this and recycling the power? or > is a reset exactly the same as powering off then on? -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

Hi Wouter, How do you manage to short the +5V line without drawing huge amounts of current and overloading the 7805? Sean At 05:25 PM 1/19/2003 +0100, you wrote: {Quote hidden}> > if so, what is the difference between doing this and > > recycling the power? or > > is a reset exactly the same as powering off then on? > >Power cycling is the more thorough reset. Some components (LCDs for >instance) don't even have a real (external) reset pin. I almost always >use a 7805 regulator and, I often use a switch that shorts the 5 Volt as >reset. > >For programming some newer PICs require MCLR rise to Vpp *before* +5 is >applied. > >Wouter van Ooijen > >-- ------------------------------------------- >Van Ooijen Technische Informatica: http://www.voti.nl >consultancy, development, PICmicro products > >-- >http://www.piclist.com hint: The PICList is archived three different >ways. See http://www.piclist.com/#archives for details. -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

Odd, don't know why that would have happened. I've replied to several this morning and all have gone to the list. Every one I've looked at (including the one to which you replied) has the OP as the From: address and the PICLIST address as the Reply-To:. Dale -- It's a thankless job, but I've got a lot of Karma to burn off. On Sun, 19 Jan 2003, Olin Lathrop wrote: > Dale, I think there is still a problem with the list reply address. I > replied to the MCLR question and got the response below from the list > server. I'm guessing that the original poster set his REPLY-TO address > and the list server substituted the list server command address instead of > the list distribution address. -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

Yes, it's better to switch the hot side, not the ground side. Dale -- It's a thankless job, but I've got a lot of Karma to burn off. On Sun, 19 Jan 2003, rad0 wrote: > I was going to put a little switch in the ground line, > or the trace, between my power jack and the 7805, > > is this OK, or is there a better more correct way... -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

Thinking about it a bit more, perhaps he uses a double throw switch, which both disconnects the 7805 from the PIC's Vdd lines and also shorts the PIC's Vdd lines. The advantage of this is that it would also make sure that any capacitors on the PIC's power pins were also shorted. You would also need to be careful that there is no way the PIC could be receiving power through it's IO pins (which is possible because of the protection diodes). Sean At 11:44 AM 1/19/2003 -0600, you wrote: >Yeah, I don't understand what this means exactly. > >I was going to put a little switch in the ground line, >or the trace, between my power jack and the 7805, > >is this OK, or is there a better more correct way... > >thanks -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

On Sun, 19 Jan 2003, rad0 wrote: > This is my second attempt at having a pc board made, > I'm sure I'll end up doing it twice. If you're not doing it yourself to gain experience and learnt he whole PCB layout & manufacturing process, I know Olimex and other places have pretty cheal PIC prototypeing/experimenter boards available. They typically have a place for a PIC with resonator or crystal, voltage regulator, RS232 interface and DB9 connector, ICSP/ICD connections and some hole grid area for experimenting. I just looked, Olimex gets all of $6.95 for a bare board. I have seen others, many of which look like good deals as well. Dale -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

> How do you manage to short the +5V line without drawing huge > amounts of > current and overloading the 7805? The current-protection will limit the curent to 2 A or so. No problem. Wouter van Ooijen -- ------------------------------------------- Van Ooijen Technische Informatica: http://www.voti.nl consultancy, development, PICmicro products -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

> You > would also > need to be careful that there is no way the PIC could be > receiving power > through it's IO pins (which is possible because of the > protection diodes). And make sure there is a resistor between MCLR and any capacitor! Wouter van Ooijen -- ------------------------------------------- Van Ooijen Technische Informatica: http://www.voti.nl consultancy, development, PICmicro products -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

On 19 Jan 2003 at 9:51, rad0 wrote: <snip> >...and I use rb6 and rb7 > thru resisters for programming via bootloader and rs232 feedback > Yes, keeping RB6 and RB7 free for in circuit programming is a good idea. A bootloader though will often use the UART for RS232 communications, or some bootloaders use a general purpose port line. I presume you are using a PIC16F87x as most other parts AFAIK don't support bootloading (apart from the 18F series). The bootloader from http://www.microchipc.com/ is cool in that it also generates a reset signal that on the serial port that you can route to MCLR. That way, to upload new code you just click the Write button and away it goes, no need to manually reset your micro. -- Brent Brown, Electronic Design Solutions 16 English Street, Hamilton, New Zealand Ph/fax: +64 7 849 0069 Mobile/txt: 025 334 069 eMail: brent.brownKILLspamclear.net.nz -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

I looked at the olimex site, and I think I found what you're talking about. But I don't see the point of the protoboard systems that are made up of plastic boards with holes only...you have to solder wires on everything, and I usually hook it up wrong once or twice, So, I use solderless breadboards, and the thing I am making is something that you can place beside the solderless breadboard, and connect the registers over to the breadboard using the normal plug in wires. and It's a bit of an exercise for me too, thanks though. {Original Message removed}

> perhaps he uses a double throw switch, which both disconnects > the 7805 from the PIC's Vdd lines and also shorts the PIC's Vdd > lines That's the best way to ensure a power-down reset. Circuits can behave oddly (don't I know it !!) if Vdd doesn't go low enough when the power switch is turned off before power is re-applied. It's recommended in the electrical specs that Vdd reaches Vss before power-up, and shorting the Vdd and Vss pins with a switch as or after the power supply is disconnected pretty much guarantees that -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

alright Jinx, what do you think of this? I now have a on off switch between the wall transformer +V and the input to the 7805 and I have a momentary (NO) switch between Vdd and Vss, to be pressed when the main switch is off, when things are acting strange, to get a complete reset. And, I've asked this before, but I've forgotten now, sorry but I have a small capacitor between the 7805 +5vdc output and ground, is this all that is required or a good idea OR what do you recommend here, the capacitors, filter out noise correct? Where else do you need to do this? thanks, {Original Message removed}

On Sun, 19 Jan 2003, rad0 wrote: *>I now have a on off switch between the wall transformer +V *>and the input to the 7805 If you use a wall transformer all you really need is a 1k resistor between Vss and Vdd. If you use batteries you want something else. The 5mA the resistor takes will discharge all power rail caps in less than a few seconds and allow proper reset at each power-on. Peter -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

> the capacitors, filter out noise correct? Where else do you > need to do this? Two things I always do - (1) on the underside of the board a 10n ceramic and a 47u electrolytic across the Vdd and Vss pins and (2) connect the crystal case to Vss. This fixed strange behaviour in at least two circuits -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.