Hysteresis on dsPIC ports?
in [Design]
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From: Jan Panteltje on 26 Jan 2010 14:55 On a sunny day (Tue, 26 Jan 2010 11:17:17 -0800) it happened Joerg <invalid(a)invalid.invalid> wrote in <7s8te0F2reU2(a)mid.individual.net>: >Jan Panteltje wrote: >> On a sunny day (Tue, 26 Jan 2010 10:28:05 -0800) it happened Joerg >> <invalid(a)invalid.invalid> wrote in <7s8qhqFig4U1(a)mid.individual.net>: >> >>>> it clearly shows min and max levels for the logical inputs. >>>> What more do you want? >>>> ftp://panteltje.com/pub/pic_io.jpg >>>> >>> This is what I want and what other mfgs provide: A min-max guaranteed >>> _spec_ for the hysteresis. >> >> >> No, that datasheet says: if the level is above .8 * Vdd then it will be a one, >> and if below .2 * Vdd it will be a zero. >> So you have < .2 * Vdd noise margin from ground and .8 * Vdd noise margin from Vdd. >> > >Unfortunately that is not what such a spec says. It essentially says >that they don't guarantee anything if you are between 0.2*VDD and >0.8*VDD. That has nothing to do with hysteresis. And most definitely not >with noise margin. No, you do not interpret this right. It says the input line noise can peak, for a 5V supply, when input is high, to Vdd .2 x 5 = 1 V below Vdd, so to >4V, and the noise on the input can peak to < +1 V when at zero. When noise stays below or above those values, the input will not flip, and the hysteresis will not happen. >Well, the guy at Microchip saw it but could not help. Because there is nothing top help, you do not understand the spec.
From: Joerg on 26 Jan 2010 15:10 Jim Thompson wrote: > On Tue, 26 Jan 2010 11:17:17 -0800, Joerg <invalid(a)invalid.invalid> > wrote: > >> Jan Panteltje wrote: >>> On a sunny day (Tue, 26 Jan 2010 10:28:05 -0800) it happened Joerg >>> <invalid(a)invalid.invalid> wrote in <7s8qhqFig4U1(a)mid.individual.net>: >>> >>>>> it clearly shows min and max levels for the logical inputs. >>>>> What more do you want? >>>>> ftp://panteltje.com/pub/pic_io.jpg >>>>> >>>> This is what I want and what other mfgs provide: A min-max guaranteed >>>> _spec_ for the hysteresis. >>> >>> No, that datasheet says: if the level is above .8 * Vdd then it will be a one, >>> and if below .2 * Vdd it will be a zero. >>> So you have < .2 * Vdd noise margin from ground and .8 * Vdd noise margin from Vdd. >>> >> Unfortunately that is not what such a spec says. It essentially says >> that they don't guarantee anything if you are between 0.2*VDD and >> 0.8*VDD. That has nothing to do with hysteresis. And most definitely not >> with noise margin. >> >> >>> From that follows the max noise you can have on the supply line and ground. >>> I do not see your problem with this spec. >> >> Well, the guy at Microchip saw it but could not help. > > Maybe do as others here have done, write an E-mail directly to Steve > Sanghi ?:-) > > It's been a couple of years since I did some oscillator design work > for them. Some of those people (I believe Don Gerber, for sure) are > still there. Tell me what part and what pin spec is your problem? > I'll ask privately. > It is this controller from their dsPIC series: DSPIC33FJ256GP710 Main thing is they should write the hysteresis min-max values into the datasheet like other manufacturers do. And most of all train their support staff a wee bit :-) -- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
From: Joerg on 26 Jan 2010 15:17 Jan Panteltje wrote: > On a sunny day (Tue, 26 Jan 2010 11:17:17 -0800) it happened Joerg > <invalid(a)invalid.invalid> wrote in <7s8te0F2reU2(a)mid.individual.net>: > >> Jan Panteltje wrote: >>> On a sunny day (Tue, 26 Jan 2010 10:28:05 -0800) it happened Joerg >>> <invalid(a)invalid.invalid> wrote in <7s8qhqFig4U1(a)mid.individual.net>: >>> >>>>> it clearly shows min and max levels for the logical inputs. >>>>> What more do you want? >>>>> ftp://panteltje.com/pub/pic_io.jpg >>>>> >>>> This is what I want and what other mfgs provide: A min-max guaranteed >>>> _spec_ for the hysteresis. >>> >>> No, that datasheet says: if the level is above .8 * Vdd then it will be a one, >>> and if below .2 * Vdd it will be a zero. >>> So you have < .2 * Vdd noise margin from ground and .8 * Vdd noise margin from Vdd. >>> >> Unfortunately that is not what such a spec says. It essentially says >> that they don't guarantee anything if you are between 0.2*VDD and >> 0.8*VDD. That has nothing to do with hysteresis. And most definitely not >> with noise margin. > > No, you do not interpret this right. > It says the input line noise can peak, for a 5V supply, > when input is high, to Vdd .2 x 5 = 1 V below Vdd, so to >4V, > and the noise on the input can peak to < +1 V when at zero. > When noise stays below or above those values, the input will not flip, > and the hysteresis will not happen. > Again, this does _not_ guarantee the input won't switch to low at, say, 1.3V or high at 3.5V. It only says that they don't guarantee it will switch there but it could (and probably does). It has nothing to do with hysteresis and noise margin. I bet Jim could elucidate. >> Well, the guy at Microchip saw it but could not help. > > Because there is nothing top help, you do not understand the spec. > Then why did they not write back that the hysteresis is 0.2*VDD to 0.8*VDD? One of the reasons is that this would still not specify a min-max hysteresis. Which you need in order to calculate noise margins properly. -- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
From: Jim Thompson on 26 Jan 2010 15:56 On Tue, 26 Jan 2010 12:17:19 -0800, Joerg <invalid(a)invalid.invalid> wrote: >Jan Panteltje wrote: >> On a sunny day (Tue, 26 Jan 2010 11:17:17 -0800) it happened Joerg >> <invalid(a)invalid.invalid> wrote in <7s8te0F2reU2(a)mid.individual.net>: >> >>> Jan Panteltje wrote: >>>> On a sunny day (Tue, 26 Jan 2010 10:28:05 -0800) it happened Joerg >>>> <invalid(a)invalid.invalid> wrote in <7s8qhqFig4U1(a)mid.individual.net>: >>>> >>>>>> it clearly shows min and max levels for the logical inputs. >>>>>> What more do you want? >>>>>> ftp://panteltje.com/pub/pic_io.jpg >>>>>> >>>>> This is what I want and what other mfgs provide: A min-max guaranteed >>>>> _spec_ for the hysteresis. >>>> >>>> No, that datasheet says: if the level is above .8 * Vdd then it will be a one, >>>> and if below .2 * Vdd it will be a zero. >>>> So you have < .2 * Vdd noise margin from ground and .8 * Vdd noise margin from Vdd. >>>> >>> Unfortunately that is not what such a spec says. It essentially says >>> that they don't guarantee anything if you are between 0.2*VDD and >>> 0.8*VDD. That has nothing to do with hysteresis. And most definitely not >>> with noise margin. >> >> No, you do not interpret this right. >> It says the input line noise can peak, for a 5V supply, >> when input is high, to Vdd .2 x 5 = 1 V below Vdd, so to >4V, >> and the noise on the input can peak to < +1 V when at zero. >> When noise stays below or above those values, the input will not flip, >> and the hysteresis will not happen. >> > >Again, this does _not_ guarantee the input won't switch to low at, say, >1.3V or high at 3.5V. It only says that they don't guarantee it will >switch there but it could (and probably does). It has nothing to do with >hysteresis and noise margin. I bet Jim could elucidate. > > >>> Well, the guy at Microchip saw it but could not help. >> >> Because there is nothing top help, you do not understand the spec. >> > >Then why did they not write back that the hysteresis is 0.2*VDD to >0.8*VDD? One of the reasons is that this would still not specify a >min-max hysteresis. Which you need in order to calculate noise margins >properly. A quick surf of DSPIC33FJ256GP710, for the data sheet, shows NO MENTION of hysteresis. What makes you think there IS hysteresis? A definition of inputs with ZERO <= 0.3*VDD and ONE >= 0.7*VDD is industry standard. ...Jim Thompson -- | James E.Thompson, CTO | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food.
From: Joerg on 26 Jan 2010 16:55
Jim Thompson wrote: > On Tue, 26 Jan 2010 12:17:19 -0800, Joerg <invalid(a)invalid.invalid> > wrote: > >> Jan Panteltje wrote: >>> On a sunny day (Tue, 26 Jan 2010 11:17:17 -0800) it happened Joerg >>> <invalid(a)invalid.invalid> wrote in <7s8te0F2reU2(a)mid.individual.net>: >>> >>>> Jan Panteltje wrote: >>>>> On a sunny day (Tue, 26 Jan 2010 10:28:05 -0800) it happened Joerg >>>>> <invalid(a)invalid.invalid> wrote in <7s8qhqFig4U1(a)mid.individual.net>: >>>>> >>>>>>> it clearly shows min and max levels for the logical inputs. >>>>>>> What more do you want? >>>>>>> ftp://panteltje.com/pub/pic_io.jpg >>>>>>> >>>>>> This is what I want and what other mfgs provide: A min-max guaranteed >>>>>> _spec_ for the hysteresis. >>>>> No, that datasheet says: if the level is above .8 * Vdd then it will be a one, >>>>> and if below .2 * Vdd it will be a zero. >>>>> So you have < .2 * Vdd noise margin from ground and .8 * Vdd noise margin from Vdd. >>>>> >>>> Unfortunately that is not what such a spec says. It essentially says >>>> that they don't guarantee anything if you are between 0.2*VDD and >>>> 0.8*VDD. That has nothing to do with hysteresis. And most definitely not >>>> with noise margin. >>> No, you do not interpret this right. >>> It says the input line noise can peak, for a 5V supply, >>> when input is high, to Vdd .2 x 5 = 1 V below Vdd, so to >4V, >>> and the noise on the input can peak to < +1 V when at zero. >>> When noise stays below or above those values, the input will not flip, >>> and the hysteresis will not happen. >>> >> Again, this does _not_ guarantee the input won't switch to low at, say, >> 1.3V or high at 3.5V. It only says that they don't guarantee it will >> switch there but it could (and probably does). It has nothing to do with >> hysteresis and noise margin. I bet Jim could elucidate. >> >> >>>> Well, the guy at Microchip saw it but could not help. >>> Because there is nothing top help, you do not understand the spec. >>> >> Then why did they not write back that the hysteresis is 0.2*VDD to >> 0.8*VDD? One of the reasons is that this would still not specify a >> min-max hysteresis. Which you need in order to calculate noise margins >> properly. > > A quick surf of DSPIC33FJ256GP710, for the data sheet, shows NO > MENTION of hysteresis. > That's the problem, it should, just like the MSP430 datasheets do. > What makes you think there IS hysteresis? > Because it says under "I/O Ports" that they have Schmitt trigger inputs. > A definition of inputs with ZERO <= 0.3*VDD and ONE >= 0.7*VDD is > industry standard. > I was hoping Jan would understand that :-) Microchip is a little more cautious there, with 0.2 and 0.8. But that does not guarantee that it won't switch at 0.3 or even 0.4. -- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM. |