From: Basham, R. R <ric...@bo...> - 2005-01-06 16:58:04
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I have a quick question regarding the following exchange. J> Secondly, I'm looking at using the I2C buss--- on the breakout=20 J> daughter card schematic, there are no pullup resistors for the I2C=20 J> bus. Are these on the gumstix board itself, or do we need to pull=20 J> these lines up to 5V ourselves somewhere? C>You need to add them yourself, as I understand it from a previous post here. =20 C>Try searching the archives for the original response on that. Can you connect the waysmall I2C bus to a 5V I2C bus? As I understand it the waysmall is running on 3.3V. Thanks, Rich -----Original Message----- From: Craig R Hughes [mailto:cr...@gu...]=20 Sent: Saturday, January 01, 2005 2:19 AM To: gum...@li... Subject: Re: [Gumstix-users] I2C Bus use with Gumstix.... Jay wrote: J> I've got an older model Gumstix. (think it might be a model D? Is=20 J> there any way to tell without opening up the waysmall box to see? I=20 J> know its not an F).... I bought it for another project, but now I=20 J> want to use it to control a robot I'm planning to build. J>=20 J> So, first question is, are the new daughter cards that have just been J> released (or are about to be released) compatible with my older=20 J> board? (And is there a way to tell which revision it is without=20 J> opening up the waysmall? I bought it from the gumstix.com store last=20 J> spring.) You can ask :) You have a -D, which is also known as a -orig. The new boards won't directly=20 connect to the -orig gumstix, but I think Gordon has a trans-connector which=20 will convert the old D connector into the new F connector. The board's=20 basically identical except for using a different connector (and the waysmall=20 buddy is slightly different too, using different GPIO lines for the USB). J> Secondly, I'm looking at using the I2C buss--- on the breakout=20 J> daughter card schematic, there are no pullup resistors for the I2C=20 J> bus. Are these on the gumstix board itself, or do we need to pull=20 J> these lines up to 5V ourselves somewhere? You need to add them yourself, as I understand it from a previous post here. =20 Try searching the archives for the original response on that. J> Thirdly, has anyone used the I2C drivers (oh, wait, are they getting=20 J> built into the current distribution?) successfully yet? Yup, a number of people have used them succesfully. J> I saw a programming example for using I2C under linux ,and you just=20 J> open to I2C device like a file and read / write to it. I'm assuming=20 J> the driver, by default, makes the linux machine the I2C bus master. I believe that's correct. J> PS-- Also, I guess I need to upgrade my bootloader before I can=20 J> upgrade the linux install, right? It's a very good idea to do so, because the original bootloader sets the RAM=20 refresh rate incorrectly, and so you might find you can't actually flash a=20 root_fs successfully until you've upgraded the u-boot. C ------------------------------------------------------- The SF.Net email is sponsored by: Beat the post-holiday blues Get a FREE limited edition SourceForge.net t-shirt from ThinkGeek. It's fun and FREE -- well, almost....http://www.thinkgeek.com/sfshirt _______________________________________________ gumstix-users mailing list gum...@li... https://lists.sourceforge.net/lists/listinfo/gumstix-users |
From: Basham, R. R <ric...@bo...> - 2005-01-07 06:27:13
|
Dave, Thanks. I have read some of these papers and that is why I asked the question. I was going to use a level shifting circuit but that message made it sound like I could make a direct connection. I thought maybe I had missed something.=20 Rich -----Original Message----- From: Dave Hylands [mailto:dhy...@gm...]=20 Sent: Thursday, January 06, 2005 9:47 AM To: gum...@li... Subject: Re: [Gumstix-users] I2C Bus use with Gumstix.... Hi Rich, > Can you connect the waysmall I2C bus to a 5V I2C bus? > As I understand it the waysmall is running on 3.3V. Be careful here. The datasheet inidcates that these pins can go above Vcc (i.e. 3.3v). This means that the pullups should only pullup to 3.3v. However, you can probably connect tje bus with 3.3 pullups to a 5v device and it will work. I2C works by using open collector outputs, so the device driving the bus either pulls the signal to ground, or doesn't, in which case the pullup pulls it back up to 3.3v. Many 5v devices (especially today) will recognize a 3.3v signal as a logic high. I haven't yet connected the i2c bus on the gumstix to a 5v device, but I've done a bunch of research into level shifting and stuff, and here's what I've come up with. In the i2c spec (http://www.semiconductors.philips.com/markets/mms/protocols/i2c/index.h tml) on page 43 they show how you can connect two busses that are running at different voltages using a couple of MOSFETs. A much more in-depth tech-note from Philips: http://www.standardproducts.philips.com/support/appnotes/i2c/pdf/an97055 .pdf A paper which analyses the MOSFET approach: http://www.mbari.org/staff/lance/N-MOSFET_bidirectional_level_shifter_an alysis.pdf Maxim makes a part designed specifically for doing i2c level translating: http://www.maxim-ic.com/quick_view2.cfm/qv_pk/3253 (just be aware that some of the parts are only rated to 230kbits, the others can all do 16 Mbits, which exceeds the 400kbits that the gumstix can do). You can get free samples from Maxim. TI also makes a part: http://focus.ti.com/docs/prod/folders/print/sn74lvc2t45.html (which is available from Digikey as part: 296-16845-1-ND) that should work. -- Dave Hylands Vancouver, BC, Canada http://www.DaveHylands.com/ ------------------------------------------------------- The SF.Net email is sponsored by: Beat the post-holiday blues Get a FREE limited edition SourceForge.net t-shirt from ThinkGeek. It's fun and FREE -- well, almost....http://www.thinkgeek.com/sfshirt _______________________________________________ gumstix-users mailing list gum...@li... https://lists.sourceforge.net/lists/listinfo/gumstix-users |
From: Dave H. <dhy...@gm...> - 2005-01-07 06:37:59
|
Hi Rich, I realized part of my post was incorrect. I said: > Be careful here. The datasheet inidcates that these pins can go above > Vcc (i.e. 3.3v). and I should have said that they can't go above Vcc. On Thu, 6 Jan 2005 22:26:59 -0800, Basham, Richard R <ric...@bo...> wrote: > Dave, > > Thanks. I have read some of these papers and that is why I asked the > question. I was going to use a level shifting circuit but that message > made it sound like I could make a direct connection. I thought maybe I > had missed something. You probably can make a direct connection, priovided the pullups only pullup to 3.3v. You just need to verify that the 5v devices work with 3.3v as the logic high. -- Dave Hylands Vancouver, BC, Canada http://www.DaveHylands.com/ |
From: Achim W. <awa...@gm...> - 2005-04-16 10:38:39
|
Hello everyone, I am refering to a mail from the archive written by Dave Hylands on January 06, 2005: > TI also makes a part: > http://focus.ti.com/docs/prod/folders/print/sn74lvc2t45.html (which is > available from Digikey as part: 296-16845-1-ND) that should work. I found out that this driver is not suitable as a (bidirectional) I2C level shifter. Having read the datasheet for the SN74lvc2t45 not thoroughly enough I missed the description of the DIR pin that controls the direction of data transfer. Integrated in an application where the gumstix sends data to a 5V I2C slave (Atmega8) the slave can receive the data but is unable to return the ACK signal by pulling the SDA line down. I haven't tried that with the gumstix yet but with two Atmega8 - one in a 3.3V circuit and the other at 5V. Anyone here in this list who has experience with the TI SN74lvc2t45? Could replacing the chip with a MAX3373 solve the problem? Regards, Achim. |
From: Andreas T. <li...@da...> - 2005-04-16 12:37:22
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> > Anyone here in this list who has experience with the TI SN74lvc2t45? > Could replacing the chip with a MAX3373 solve the problem? > I think the MAX3373 should work great for your purpose. Also this chip http://focus.ti.com/docs/prod/folders/print/pca9306.html should do the job. I'm planning to use the PCA9306 on a robostix like board. Regards, Andreas |
From: Achim W. <awa...@gm...> - 2005-04-16 13:53:37
|
Andreas, thanks for the info. The PCA9306 looks good (even though it's not pin-compatible with the SN74lvc2t45 ;-) Do you have an idea where to buy it or the MAX3373 in Germany/Austria (besides ordering samples)? Not even Digikey has it in the offer. Servus, Achim. Andreas Trenkwalder wrote: >I think the MAX3373 should work great for your purpose. Also this chip >http://focus.ti.com/docs/prod/folders/print/pca9306.html should do the job. >I'm planning to use the PCA9306 on a robostix like board. > >Regards, >Andreas > > |
From: Andreas T. <li...@da...> - 2005-04-16 14:27:11
|
> > Do you have an idea where to buy it or the MAX3373 in Germany/Austria > (besides ordering samples)? Not even Digikey has it in the offer. > Really good question. I looked in varios onlineshops with no luck. Try to cantact Maxim directly: http://www.maxim-ic.com/company/contact/sales_offices_en.cfm/filter/isale lG, Andreas |
From: Dave H. <dhy...@gm...> - 2005-01-06 17:47:34
|
Hi Rich, > Can you connect the waysmall I2C bus to a 5V I2C bus? > As I understand it the waysmall is running on 3.3V. Be careful here. The datasheet inidcates that these pins can go above Vcc (i.e. 3.3v). This means that the pullups should only pullup to 3.3v. However, you can probably connect tje bus with 3.3 pullups to a 5v device and it will work. I2C works by using open collector outputs, so the device driving the bus either pulls the signal to ground, or doesn't, in which case the pullup pulls it back up to 3.3v. Many 5v devices (especially today) will recognize a 3.3v signal as a logic high. I haven't yet connected the i2c bus on the gumstix to a 5v device, but I've done a bunch of research into level shifting and stuff, and here's what I've come up with. In the i2c spec (http://www.semiconductors.philips.com/markets/mms/protocols/i2c/index.html) on page 43 they show how you can connect two busses that are running at different voltages using a couple of MOSFETs. A much more in-depth tech-note from Philips: http://www.standardproducts.philips.com/support/appnotes/i2c/pdf/an97055.pdf A paper which analyses the MOSFET approach: http://www.mbari.org/staff/lance/N-MOSFET_bidirectional_level_shifter_analysis.pdf Maxim makes a part designed specifically for doing i2c level translating: http://www.maxim-ic.com/quick_view2.cfm/qv_pk/3253 (just be aware that some of the parts are only rated to 230kbits, the others can all do 16 Mbits, which exceeds the 400kbits that the gumstix can do). You can get free samples from Maxim. TI also makes a part: http://focus.ti.com/docs/prod/folders/print/sn74lvc2t45.html (which is available from Digikey as part: 296-16845-1-ND) that should work. -- Dave Hylands Vancouver, BC, Canada http://www.DaveHylands.com/ |