Whoever designed your board ignored that, so can't really complain that it now doesn't work. Oops.ID_SD and ID_SC PINS:
These pins are reserved for ID EEPROM.
At boot time this I2C interface will be
interrogated to look for an EEPROM
that identifes the attached board and
allows automagic setup of the GPIOs
(and optionally, Linux drivers).
DO NOT USE these pins for anything other
than attaching an I2C ID EEPROM. Leave
unconnected if ID EEPROM not required
Eh?mgregg wrote: I find it disappointing that the specification was changed in a way that breaks older hats.
Turning off i2c_vc=on opens /dev/i2c-1 only. But that port doesn't find anything on that bus if they are plugged into pins 3&5.6by9 wrote:I think bensimmo is probably correct - the very original rev1 PiB 256MB did bring out i2c-0 to pins 3&5 on the 26pin header and your old boards are probably rev1. That changed when production was brought back to the UK, so Sept 2012. All subsequent boards (A+, B+, B2, B3, and Zero) have had i2c-1 on those pins.
The simple answer is do NOT enable i2c_vc=on on a Pi3 - bad things will happen. The 0x43 you are seeing is the GPIO expander (which slightly confuses me as I would have expected pin muxing woes resulting in nothing detected rather than seeing the expander).
/dev/i2c-1 is brought out on pins 3&5 of the 40 pin header, and that is available for use by your application.
If you need to support both, then you will need to check the board revision yourself and open /dev/i2c-0 or /dev/i2c-1 based on that. In neither case should you need i2c_vc=on, as i2c_arm=on will enable the correct device for your board revision.
Correct. i2c_arm=on will enable /dev/i2c-1 on all revisions of the Pi, except on the 256MB rev1 model B from 2012 where it enables i2c-0.mgregg wrote:Turning off i2c_vc=on opens /dev/i2c-1 only.
Details of what you've done then. Many many people are using i2c-1 on pins 3&5 without issue.mgregg wrote:But that port doesn't find anything on that bus if they are plugged into pins 3&5.
You need to provide a load more information then. No one else can see your setup.mgregg wrote:I'll be happy if you can prove me wrong.
Sorry, that is absolute twaddle.mgregg wrote:It looks as though if you have i2c on pins 3&5, without software i2c, you cannot use those devices.
It's also possible to use wiringPi's "gpio readall" command** to provide a similar check.6by9 wrote: ...
- Check with "sudo raspi-gpio --get" that GPIOs 2&3 are assigned to ALT0 and therefore SDA1 and SCL1. No other GPIOs should be assigned to the SDA1 or SCL1 function, otherwise you will get issues.
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