From: Francisco Aguerre <[email protected]> Reply-To: <[email protected]> Date: Thursday, June 5, 2014 at 12:06 PM To: <[email protected]> Subject: [beagleboard] Re: I2C pull-ups while BBB is powered off
> Charles, > > Thanks for your response. > > I read the section you mentioned from the I2C standard and it seems that, for > this to work properly, there has to be pull-up resistors on both sides of the > FET, which doesn't solve my problem. Maybe I didn't understand something, but > if I don't pull-up the I2C pins of the BBB, the lines will never go high, > because the FET will be in its off state. > > I want to avoid pulling the I/O pins high before the BBB is fully powered on. http://www.ti.com/product/TXS0102?keyMatch=txs&tisearch=Search-EN Regards, John > > > On Thursday, June 5, 2014 12:47:53 PM UTC-3, Francisco Aguerre wrote: >> Hi everyone, >> >> I'm trying to interface a RTC with my BBB using the I2C bus. The reference >> manual states that none of the pins in the expansion connectors should be >> driven while the system is not powered on. I have isolated other inputs using >> tristate buffers and the SYS_RESETn, but the I2C lines, being bidirectional >> is a bit trickier. Is it necessary in this case to isolate the lines during >> power up? I'm connecting the pull-ups to the +3v3 pin on the expansion >> connector. >> >> If I should isolate the lines, what's the best method? I'm thinking of using >> a cmos switch to disconnect the resistors during power up, but maybe there >> are better ideas. >> >> Thnaks! > > -- > For more options, visit http://beagleboard.org/discuss > --- > You received this message because you are subscribed to the Google Groups > "BeagleBoard" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected]. > For more options, visit https://groups.google.com/d/optout. -- For more options, visit http://beagleboard.org/discuss --- You received this message because you are subscribed to the Google Groups "BeagleBoard" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. For more options, visit https://groups.google.com/d/optout.
