Hysteresis on dsPIC ports?
in [Design]
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From: Jim Thompson on 26 Jan 2010 17:03 On Tue, 26 Jan 2010 13:55:54 -0800, Joerg <invalid(a)invalid.invalid> wrote: >Jim Thompson wrote: >> On Tue, 26 Jan 2010 12:17:19 -0800, Joerg <invalid(a)invalid.invalid> >> wrote: >> [snip] >> >> 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. I searched for "hysteresis". Nowhere is that mentioned. I'll ask. But I'm pretty sure what I'll find is it's simply to clean up slow inputs. ...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 17:50 Jim Thompson wrote: > On Tue, 26 Jan 2010 13:55:54 -0800, Joerg <invalid(a)invalid.invalid> > wrote: > >> Jim Thompson wrote: >>> On Tue, 26 Jan 2010 12:17:19 -0800, Joerg <invalid(a)invalid.invalid> >>> wrote: >>> > [snip] >>> 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. > > I searched for "hysteresis". Nowhere is that mentioned. I'll ask. > > But I'm pretty sure what I'll find is it's simply to clean up slow > inputs. > Usually that's the reason, reduces the "oh s..t, it don't work" support requests. But if you need it for noise immunity purposes the hysteresis would have to be known. That's where I must say that TI is a lot more diligent in their specs. Any old thunderstorm would blow a 50mV hysteresis aside but not a 500mV one. Right now about half my assignments are redesigns. Not always fun but it's got to be done. -- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
From: Fred Bartoli on 26 Jan 2010 17:57 Joerg a �crit : > Jim Thompson wrote: >> On Tue, 26 Jan 2010 13:55:54 -0800, Joerg <invalid(a)invalid.invalid> >> wrote: >> >>> Jim Thompson wrote: >>>> On Tue, 26 Jan 2010 12:17:19 -0800, Joerg <invalid(a)invalid.invalid> >>>> wrote: >>>> >> [snip] >>>> 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. >> >> I searched for "hysteresis". Nowhere is that mentioned. I'll ask. >> >> But I'm pretty sure what I'll find is it's simply to clean up slow >> inputs. >> > > Usually that's the reason, reduces the "oh s..t, it don't work" support > requests. But if you need it for noise immunity purposes the hysteresis > would have to be known. That's where I must say that TI is a lot more > diligent in their specs. Any old thunderstorm would blow a 50mV > hysteresis aside but not a 500mV one. Right now about half my > assignments are redesigns. Not always fun but it's got to be done. > Cute! Where do you get those 500mV lightning? ;-) -- Thanks, Fred.
From: Jim Thompson on 26 Jan 2010 18:01 On Tue, 26 Jan 2010 14:50:56 -0800, Joerg <invalid(a)invalid.invalid> wrote: >Jim Thompson wrote: >> On Tue, 26 Jan 2010 13:55:54 -0800, Joerg <invalid(a)invalid.invalid> >> wrote: >> [snip] >>> >>> 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. >> >> I searched for "hysteresis". Nowhere is that mentioned. I'll ask. >> >> But I'm pretty sure what I'll find is it's simply to clean up slow >> inputs. >> > >Usually that's the reason, reduces the "oh s..t, it don't work" support >requests. But if you need it for noise immunity purposes the hysteresis >would have to be known. That's where I must say that TI is a lot more >diligent in their specs. Any old thunderstorm would blow a 50mV >hysteresis aside but not a 500mV one. I'd expect about a VT (or around 0.35V) for this sort of animal. >Right now about half my >assignments are redesigns. Not always fun but it's got to be done. A lot of my work is fixing the errors/blunders of others. Somewhat shocking, I sent a blanket E-mail to about a dozen names I knew from my Microchip oscillator days. Four of them came back "unknown" :-( ...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 18:02
Fred Bartoli wrote: > Joerg a �crit : >> Jim Thompson wrote: >>> On Tue, 26 Jan 2010 13:55:54 -0800, Joerg <invalid(a)invalid.invalid> >>> wrote: >>> >>>> Jim Thompson wrote: >>>>> On Tue, 26 Jan 2010 12:17:19 -0800, Joerg <invalid(a)invalid.invalid> >>>>> wrote: >>>>> >>> [snip] >>>>> 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. >>> >>> I searched for "hysteresis". Nowhere is that mentioned. I'll ask. >>> >>> But I'm pretty sure what I'll find is it's simply to clean up slow >>> inputs. >>> >> >> Usually that's the reason, reduces the "oh s..t, it don't work" >> support requests. But if you need it for noise immunity purposes the >> hysteresis would have to be known. That's where I must say that TI is >> a lot more diligent in their specs. Any old thunderstorm would blow a >> 50mV hysteresis aside but not a 500mV one. Right now about half my >> assignments are redesigns. Not always fun but it's got to be done. >> > > Cute! Where do you get those 500mV lightning? ;-) > It's the SMT version, from 0805-size clouds :-) What I meant is inside a circuit. A properly terminated trace always picks up some, but not a whole lot. So when you have signals that aren't terribly fast you can easily get a double pulse and it knocks some routine off the rocker. -- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM. |