From PICLIST@MITVMA.MIT.EDU Fri Nov 15 14:33:02 2002 Received: from cherry.ease.lsoft.com [209.119.0.109] by dpmail10.doteasy.com with ESMTP (SMTPD32-7.13) id A61E2080144; Fri, 15 Nov 2002 14:33:02 -0800 Received: from PEAR.EASE.LSOFT.COM (209.119.0.19) by cherry.ease.lsoft.com (LSMTP for Digital Unix v1.1b) with SMTP id <1.007DDDE0@cherry.ease.lsoft.com>; Fri, 15 Nov 2002 17:18:51 -0500 Received: from MITVMA.MIT.EDU by MITVMA.MIT.EDU (LISTSERV-TCP/IP release 1.8d) with spool id 9757 for PICLIST@MITVMA.MIT.EDU; Fri, 15 Nov 2002 17:18:32 -0500 Received: from MITVMA (NJE origin SMTP@MITVMA) by MITVMA.MIT.EDU (LMail V1.2d/1.8d) with BSMTP id 2124; Fri, 15 Nov 2002 17:18:12 -0500 Received: from *unknown [199.185.220.236] by mitvma.mit.edu (IBM VM SMTP Level 320) via TCP with SMTP ; Fri, 15 Nov 2002 17:18:11 EST X-Warning: mitvma.mit.edu: Host *unknown claimed to be priv-edtnes03-hme0.telusplanet.net Received: from dar.planet.eon.net ([66.222.146.95]) by priv-edtnes03-hme0.telusplanet.net (InterMail vM.5.01.04.05 201-253-122-122-105-20011231) with ESMTP id <20021115221811.RCW5285.priv-edtnes03-hme0.telusplanet.net@dar.planet.eon.ne t> for ; Fri, 15 Nov 2002 15:18:11 -0700 X-Sender: dwayner@pop.telusplanet.net X-Mailer: QUALCOMM Windows Eudora Version 4.3.2 Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii"; format=flowed Message-ID: <4.3.2.7.2.20021115150001.02c70da0@pop.telusplanet.net> Date: Fri, 15 Nov 2002 15:18:04 -0700 Reply-To: pic microcontroller discussion list Sender: pic microcontroller discussion list From: Dwayne Reid Subject: Re: [PIC]: 16F627 brown out? question To: PICLIST@MITVMA.MIT.EDU In-Reply-To: <004b01c28c23$51b8ba40$6501a8c0@potshe01.pa.comcast.net> X-RCPT-TO: Status: R X-UIDL: 277600743 X-Evolution-Source: pop://mailinglist%40farcite.net@mail.farcite.net/ X-Evolution: 000007ac-0000 At 04:18 PM 11/14/02 -0500, Scott Touchton wrote: >Hello List, > >I have a 16F627 that appears to be sitting in some form of brownout. The >oscillator is running, but she ceased executing code. > >Unfortunately, none of the fancy power up controls are enabled. MCLR is >disabled in the program fuses, along with the brown out detect and the >power up timers. (Don't shoot me... I inherited the design. Did I >remember to tell you that the power supply powers up and down twice a >second!!!!!) > > From this I gather she has gone into a brown out mode. Here is my exact > question: If in brown out, will the WDT cease to function? Or should > it apply a reset and get everything running again??? Since you are not using any form of brown-out detector, I'd say YES, you have a problem. I've had major problems occur if I allow a PIC's power supply to drop to about 0.7V, then restore back to normal. The chip does not function correctly and the internal watchdog does NOT correct the problem. The only sure cure is to allow Vdd to collapse all the way to 0V, then re-apply power. I've verified that I can cause this to happen on the 16c71, 16c73, 12c508. I have not had occasion to test other chips for the same problem (yet). My solution is to ALWAYS have an external power-up reset controller. I use a variety of techniques, ranging from dedicated supervisor chips (high end projects) through to simple power supply controllers (hold Vdd @ 0V until supply is high enough, then apply Vdd to the circuit). Most of my stuff is used in noisy, nasty environments. I spend a lot of time ensuring that the power supply is clean and turns on monotonically. The extra parts cost hardly anything and I don't have to worry about having thousands or tens of thousands of units coming back. The easy way for you to test if this is the problem is to do whatever it takes to get the chip to misbehave, then briefly short Vdd to Gnd. If the chip comes to life, you have found the probable cause. The fix may be as simple as adding a single J-FET and 1 resistor. Grab a J176 or J177 fet, connect S to GND, connect D to Vdd and feed G from the input of your regulator circuit via a 1M0 resistor. While the supply is less than the gate threshold of the FET, the FET looks like a low value resistance load on the supply. Once the supply is above the threshold, the FET turns off. dwayne -- Dwayne Reid Trinity Electronics Systems Ltd Edmonton, AB, CANADA (780) 489-3199 voice (780) 487-6397 fax Celebrating 18 years of Engineering Innovation (1984 - 2002) .-. .-. .-. .-. .-. .-. .-. .-. .-. .- `-' `-' `-' `-' `-' `-' `-' `-' `-' Do NOT send unsolicited commercial email to this email address. This message neither grants consent to receive unsolicited commercial email nor is intended to solicit commercial email. -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.