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Using more than one I2C bus on Overo

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Using more than one I2C bus on Overo

rink113
I'm interested in having two separate I2C busses on a project I'm building with the Overo. It is my understanding that the OMAP processor has 3 such busses. I understand that i2c-1 is used for internal power management, i2c-3 is available for the user (and I'm successfully using it), but what about i2c-2? Can it be made available simply be creating the correct device file and muxing the correct pins to the header I'm using? Just curious. Or is it, by chance, reserved for internal purposes as well and not available? I've tried looking and searching and I have not yet found an answer on this. Any help would be appreciated.
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Re: Using more than one I2C bus on Overo

JamesAng
rink113 wrote
I'm interested in having two separate I2C busses on a project I'm building with the Overo. It is my understanding that the OMAP processor has 3 such busses. I understand that i2c-1 is used for internal power management, i2c-3 is available for the user (and I'm successfully using it), but what about i2c-2? Can it be made available simply be creating the correct device file and muxing the correct pins to the header I'm using? Just curious. Or is it, by chance, reserved for internal purposes as well and not available? I've tried looking and searching and I have not yet found an answer on this. Any help would be appreciated.
If it's not on the expansion headers, I don't think it's available to enduser.
Why would you need a separate bus (except for high, constant load) since I2C is a shared, multi-devices bus.

James Ang.
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Re: Using more than one I2C bus on Overo

rink113
JamesAng wrote
If it's not on the expansion headers, I don't think it's available to enduser.
Why would you need a separate bus (except for high, constant load) since I2C is a shared, multi-devices bus.

James Ang.
I may need another I2C bus because I may be introducing another device in my design that uses I2C but runs on a different logic level voltage than my other I2C bus, and may run at a different frequency. I'm already using logic level converters for the first bus, but I'm not sure I should do it twice on the same bus (a knowledgeable friend was trying to steer me away from that). As for I/O not being available on the headers, I just finished a few weeks ago changing the MUX on the Gumstix to allow for UART2 to be available on the header instead of a few generic I/O ports so that I can use all 3 UARTS in my design -- the processor has more I/O than is routed out to pins and can be controlled via configuration. I know the other I2C bus CAN be muxed to other pins, I don't recall if I checked that the other pins it can be routed to are on headers of what I'm using (Pinto-TH) -- I should check that, otherwise, it doesn't matter if I can MUX it or not.

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Re: Using more than one I2C bus on Overo

JamesAng
rink113 wrote
I may need another I2C bus because I may be introducing another device in my design that uses I2C but runs on a different logic level voltage than my other I2C bus, and may run at a different frequency. I'm already using logic level converters for the first bus, but I'm not sure I should do it twice on the same bus (a knowledgeable friend was trying to steer me away from that).
On the strict condition of running at the same frequency, I've tried using on the same bus with 2 different logic levelers to multi-devices. So far as good. (^^,)

Do correct me if this is a technical & engineering taboos design..

rink113 wrote
As for I/O not being available on the headers, I just finished a few weeks ago changing the MUX on the Gumstix to allow for UART2 to be available on the header instead of a few generic I/O ports so that I can use all 3 UARTS in my design -- the processor has more I/O than is routed out to pins and can be controlled via configuration. I know the other I2C bus CAN be muxed to other pins, I don't recall if I checked that the other pins it can be routed to are on headers of what I'm using (Pinto-TH) -- I should check that, otherwise, it doesn't matter if I can MUX it or not.
Search the forum archives for past discussion on using all UART ports via MUX.

James Ang.
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Re: Using more than one I2C bus on Overo

rink113
JamesAng wrote
On the strict condition of running at the same frequency, I've tried using on the same bus with 2 different logic levelers to multi-devices. So far as good. (^^,)

Do correct me if this is a technical & engineering taboos design..
Wow! well, then I may very well try this approach if this has worked for you that does simplify things!

JamesAng wrote
Search the forum archives for past discussion on using all UART ports via MUX.

James Ang.
Actually I was part of that discussion. I was indeed able to change the MUX and make all UARTS available for my project. I was hoping to do the same with the other I2C bus, but the other problem is there is no device file for that other I2C bus and I don't know how to get it to appear.

You've given me some encouragement to try two level conversions on the same bus so I may very well try this.

Rink113
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Re: Using more than one I2C bus on Overo

JamesAng
rink113 wrote
JamesAng wrote
On the strict condition of running at the same frequency, I've tried using on the same bus with 2 different logic levelers to multi-devices. So far as good. (^^,)

Do correct me if this is a technical & engineering taboos design..
Wow! well, then I may very well try this approach if this has worked for you that does simplify things!
If my memory serves me correctly, I believe there is 2 different voltage leveler with a Tobi + Caspa setup.
Go take a look at the 2 schematics.

Best of luck~!

James Ang.
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