In article <1187808526.744654.296830@r23g2000prd.googlegroups.com>, mmihai says...> On Aug 22, 11:08 am, Tauno Voipio <tauno.voi...@INVALIDiki.fi> wrote: > > > It is allowed that a station in the I2C bus clamps > > a signal to ground. If you're attempting to precharge > > a clamped signal, you'll create a straight short - not > > a too recommendable practice. > > > > The clamping can be done on both the SCK and the SDA > > line. > > Yes, I know. > > Read the "simple bus" description form the article. > > I never claimed this is better than I2C from the original spec. > It is just a way to run I2C in some /special/ cases as stated in the > text.I think the problem is people are having trouble envisioning any case in which it makes sense to leave the resistors out. Robert -- Posted via a free Usenet account from http://www.teranews.com
I2C without resistors
Started by ●August 22, 2007
Reply by ●August 22, 20072007-08-22
Reply by ●August 22, 20072007-08-22
Robert Adsett wrote:> In article <1187808526.744654.296830@r23g2000prd.googlegroups.com>, > mmihai says... > >>On Aug 22, 11:08 am, Tauno Voipio <tauno.voi...@INVALIDiki.fi> wrote: >> >> >>>It is allowed that a station in the I2C bus clamps >>>a signal to ground. If you're attempting to precharge >>>a clamped signal, you'll create a straight short - not >>>a too recommendable practice. >>> >>>The clamping can be done on both the SCK and the SDA >>>line. >> >>Yes, I know. >> >>Read the "simple bus" description form the article. >> >>I never claimed this is better than I2C from the original spec. >>It is just a way to run I2C in some /special/ cases as stated in the >>text. > > > I think the problem is people are having trouble envisioning any case in > which it makes sense to leave the resistors out. > > Robert >If you made, say, 1 billion somethings, you could save about $1,000,000 Cheers Terry
Reply by ●August 23, 20072007-08-23
In article <1187829284.987009@ftpsrv1>, Terry Given says...> Robert Adsett wrote: > > In article <1187808526.744654.296830@r23g2000prd.googlegroups.com>, > > mmihai says... > > > >>On Aug 22, 11:08 am, Tauno Voipio <tauno.voi...@INVALIDiki.fi> wrote: > >> > >> > >>>It is allowed that a station in the I2C bus clamps > >>>a signal to ground. If you're attempting to precharge > >>>a clamped signal, you'll create a straight short - not > >>>a too recommendable practice. > >>> > >>>The clamping can be done on both the SCK and the SDA > >>>line. > >> > >>Yes, I know. > >> > >>Read the "simple bus" description form the article. > >> > >>I never claimed this is better than I2C from the original spec. > >>It is just a way to run I2C in some /special/ cases as stated in the > >>text. > > > > > > I think the problem is people are having trouble envisioning any case in > > which it makes sense to leave the resistors out. > > > > If you made, say, 1 billion somethings, you could save about $1,000,000Of course you won't need very many support calls or warranty claims to eat that right back up and more. Robert -- Posted via a free Usenet account from http://www.teranews.com
Reply by ●August 23, 20072007-08-23
Robert Adsett wrote:> In article <1187829284.987009@ftpsrv1>, Terry Given says... > >>Robert Adsett wrote: >> >>>In article <1187808526.744654.296830@r23g2000prd.googlegroups.com>, >>>mmihai says... >>> >>> >>>>On Aug 22, 11:08 am, Tauno Voipio <tauno.voi...@INVALIDiki.fi> wrote: >>>> >>>> >>>> >>>>>It is allowed that a station in the I2C bus clamps >>>>>a signal to ground. If you're attempting to precharge >>>>>a clamped signal, you'll create a straight short - not >>>>>a too recommendable practice. >>>>> >>>>>The clamping can be done on both the SCK and the SDA >>>>>line. >>>> >>>>Yes, I know. >>>> >>>>Read the "simple bus" description form the article. >>>> >>>>I never claimed this is better than I2C from the original spec. >>>>It is just a way to run I2C in some /special/ cases as stated in the >>>>text. >>> >>> >>>I think the problem is people are having trouble envisioning any case in >>>which it makes sense to leave the resistors out. >>> >> >>If you made, say, 1 billion somethings, you could save about $1,000,000 > > > Of course you won't need very many support calls or warranty claims to > eat that right back up and more. > > Robertabsolutely. This is a pretty good example of a *really* terrible idea. It saves $0.002 worth of resistors, brutally violates the I2C spec, and doubtless has some interesting dynamic implications. Why stop there - why not power the I2C peripheral via SCL, SDA using its internal ESD diodes, and ensuring that there is enough bus activity to keep the supply pumped up..... Cheers Terry
Reply by ●August 23, 20072007-08-23
Terry Given wrote:> absolutely. This is a pretty good example of a *really* terrible idea. > It saves $0.002 worth of resistors, brutally violates the I2C spec, and > doubtless has some interesting dynamic implications.I couldn't agree more. Why would anyone want to do this ? Graham
Reply by ●August 23, 20072007-08-23
Eeyore <rabbitsfriendsandrelations@hotmail.com> writes:> Why would anyone want to do this ?Well, in the original article, he admitted that he just forgot to design them in, and didn't want to uglify the board with a couple of afterthought resistors. I agree it's a bad idea, but he did go through all the math and engineering to see if it would work reliably enough for his purposes. Me, I'm following a friend's advice and putting a grid of solder pads on the back of my boards to add 0603 or SOIC parts later if needed. At least they're less visible that way.
Reply by ●August 23, 20072007-08-23
DJ Delorie wrote:> Eeyore <rabbitsfriendsandrelations@hotmail.com> writes: > > Why would anyone want to do this ? > > Well, in the original article, he admitted that he just forgot to > design them inThat's a bit like forgetting to tie your shoelaces ! Graham
Reply by ●August 23, 20072007-08-23
On Aug 23, 2:53 pm, Terry Given <my_n...@ieee.org> wrote:> Robert Adsett wrote: > > In article <1187829284.987009@ftpsrv1>, Terry Given says... > > >>Robert Adsett wrote: > > >>>In article <1187808526.744654.296...@r23g2000prd.googlegroups.com>, > >>>mmihai says... > > >>>>On Aug 22, 11:08 am, Tauno Voipio <tauno.voi...@INVALIDiki.fi> wrote: > > >>>>>It is allowed that a station in the I2C bus clamps > >>>>>a signal to ground. If you're attempting to precharge > >>>>>a clamped signal, you'll create a straight short - not > >>>>>a too recommendable practice. > > >>>>>The clamping can be done on both the SCK and the SDA > >>>>>line. > > >>>>Yes, I know. > > >>>>Read the "simple bus" description form the article. > > >>>>I never claimed this is better than I2C from the original spec. > >>>>It is just a way to run I2C in some /special/ cases as stated in the > >>>>text. > > >>>I think the problem is people are having trouble envisioning any case in > >>>which it makes sense to leave the resistors out. > > >>If you made, say, 1 billion somethings, you could save about $1,000,000 > > > Of course you won't need very many support calls or warranty claims to > > eat that right back up and more. > > > Robert > > absolutely. This is a pretty good example of a *really* terrible idea. > It saves $0.002 worth of resistors, brutally violates the I2C spec, and > doubtless has some interesting dynamic implications. Why stop there - > why not power the I2C peripheral via SCL, SDA using its internal ESD > diodes, and ensuring that there is enough bus activity to keep the > supply pumped up.....Works a treat with CMOS logic, just keep at least one input high at all times, don't draw too much current, keep your speeds low, and don't rely on meeting the specs :-> Ick! Dave.
Reply by ●August 23, 20072007-08-23
"mmihai" <iiahim@yahoo.com> schreef in bericht news:1187808526.744654.296830@r23g2000prd.googlegroups.com...> On Aug 22, 11:08 am, Tauno Voipio <tauno.voi...@INVALIDiki.fi> wrote: > >> It is allowed that a station in the I2C bus clamps >> a signal to ground. If you're attempting to precharge >> a clamped signal, you'll create a straight short - not >> a too recommendable practice. >> >> The clamping can be done on both the SCK and the SDA >> line. > > Yes, I know. > > Read the "simple bus" description form the article. > > I never claimed this is better than I2C from the original spec. > It is just a way to run I2C in some /special/ cases as stated in the > text. > > -- > mmihai > >Once had to add a device to such a "special". Nothing documented but "I2C". So, the bitbanging master did not look after ACKs and crashed when the clock pulse was stretched. Also bus resistance was too high as was bus capacitance. Could only survive by by adding too low pullup resistors so violating the specs a little bit more. Then added a 82B715 to isolate my own part of the bus. Which was the easy part. Programming around the other violations took some more time. So I can't but repeate it's bad engineering practice. Stick to the specs as long as you can. Preferable a little bit longer. petrus bitbyter
Reply by ●August 23, 20072007-08-23
On Aug 23, 1:17 am, Eeyore <rabbitsfriendsandrelati...@hotmail.com> wrote:> DJ Delorie wrote: > > Eeyore <rabbitsfriendsandrelati...@hotmail.com> writes: > > > Why would anyone want to do this ? > > > Well, in the original article, he admitted that he just forgot to > > design them in > > That's a bit like forgetting to tie your shoelaces !Actually, he didn't forget them, he thought the MCU had them built in. A mistake, don't we all make mistakes?
