From: kuntushi <kun...@ya...> - 2008-08-12 00:29:57
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Thanks for the info Richard. I don't think I'll need the analyser though, the CRO I have here does I2C analysing on it and I can see the clock and data lines nicely. It definitely seems that my camera chip isn't pulling the data line low. It seems like the gumstix is always asserting on that line though, so I'm wondering if maybe my pull ups aren't right or something like that. Assuming that the camera chip is working and there is a connection between the SDA and SCL lines, can anyone think of any other reason the slave wouldn't pull the data line low? Or even suggestions for trying to fix it. I'll try some higher pull ups and some other stuff now, but any other ideas would be greatly appreciated. rtstofer wrote: > > I would be surprised if the Verdex 'waited' for the 9th or ACK bit. It > expects that bit to be properly set at the next clock following the R/W > bit. If the data line isn't pulled low (ACK) then the controller > interprets the signal as a NAK and stops. Pretty consistent with what > you are seeing. > > Assuming the hardware is proper (I2C bus voltage, pull-up resistors, > connections, etc), about the only thing that can prevent the ACK bit is > an address mismatch. > > If you can see the transaction on a scope, look at the 9th bit. If it > isn't pulled low, the Verdex sees a NAK. > > I have never had much success using the I2C bus without using a logic > analyzer. I use http://www.sump.org/projects/analyzer/ based on > http://www.digilentinc.com/Products/Detail.cfm?Prod=S3BOARD I built a > little logic level shifter PCB that plugs in to the S3 board so I could > use 5V signals with a 3.3V FPGA. > > I also have a little schematic for a 2 chip synchronizer that is used to > sync a scope as it detects the start and stop condition on the bus. I > haven't used the circuit but it seems like a neat design and a great > idea. At least the scope trace will line up with the start condition. > > After 3 different attempts to attach the schematic, I have given up. If > you need it, send me an email off-list and I will attach it to a Reply. > > My email address is: rstofer "AT" pacbell "DOT" net > > Richard > > -- View this message in context: http://www.nabble.com/I2C-Setup-for-Verdex-tp18807158p18936203.html Sent from the Gumstix mailing list archive at Nabble.com. |