-------------------------------------------------- From: "Philip Pemberton" Sent: Thursday, September 23, 2010 2:10 AM To: "Microcontroller discussion list - Public." Subject: [PIC] A catalogue of cock-ups > Posted under PIC because this rather long rant relates directly to my > frustrations with the J-series PICs. > > I've been prototyping some new hardware, based around a PIC18F85J50 and > an FPGA. The FPGA handles the number crunching, the PIC is a > general-purpose garden-variety USB to parallel bridge with some smarts > (the FPGA allows it to share the ACQ RAM). > > The FPGA, however, is not the problem. The PIC is. > > > 1) The pin-one marker on my parts is ambiguous. > There are two round depressions in the chip face; one is a moulding > mark, the other is the Pin 1 marker. How do you tell them apart? Hold > the chip with the text horizontal and the Microchip logo at the top. Pin > 1 is at the bottom left. Also, the moulding mark has a bit of text > inside it, though you need a strong magnifier and a bit of chalk (or a > paint marker and some IPA) to see it. > > This cost me one chip. =A34 down the pan. Thanks, Microchip. > > > 2) The MCLR pin can't handle 12V. > MCLR on these chips is specced to run at about 5V *absolute maximum*. > The real limit is Vdd (usually 3.3V). If you change the device type > during an MPLAB run, MPLAB may not save that device type if it crashes... > > I just had an MPLAB crash. Restarted, and selected the PICKit2. MPLAB > had reselected the PIC18F252 I was using before. BANG goes another chip. > =A38 down the pan. > > I think I'm going to solder a 4.1V Zener diode across the MCLR test pad > and a conveniently located ground via... > > Tomorrow I get to fire up the SMD workstation and replace this chip. > Which is going to be great fun since it's surrounded by 0603 decoupling > capacitors and my vacuum pick-up pen is shot. Blu-tak on a cocktail > stick, anyone? > > And I haven't even gotten to a point where I could upload the LED > blinker or FPGA boot test code yet. > > AARGH. Sometimes it's just not worth chewing through the leather straps > in the morning... I'm going to bed. lol, I know how you feel... Doing a similar kind of thing with a PIC18F24J50 and an FPGA at the moment= =20 too - has had it's share of mishaps also (though it's working very well now= )=20 but that's all part of the fun... :-) It does bug me that some manufacturers don't make pin 1 less ambiguous -=20 doesn't seem that difficult to do yet everyone does it differently -=20 bevelled edges, dots, depressions, bars, text etc etc... I quite like the J series though from first experience with stuff like the= =20 remappable peripherals, although I'm using an ICD3 which I prefer to my=20 PicKit2 nowadays - seems very reliable, programs real quick and debugs well= ..=20 Also on the 18F24J50 pin 1 is marked well with a single round depression.=20 --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .