PS I2C interfacing with Zynq ZC702

[shashipoddar19]

I am trying to connect an I2C sensor with ZC702, through the TCA6416 (U80-IO expander) provided at the board. However, it has been mentioned in the datasheet that it requires the IIC_PMOD [0:7] to be connected to a Pmod peripheral module.  

Does this mean that the Development board cannot be used independently to a device without any external device? Is there any application note on the same?

[achutha]

Hi,

Please refer to this XAPP, which used the FMC IIC.

http://www.xilinx.com/support/documentation/application_notes/xapp794-1080p60-camera.pdf


Regards,
Achutha

[shashipoddar19]

We have interfaced the HDMI and EEPROM with the I2C, but the main issue is with interfacing of an I2C sensor to be connected through the IO expander. 

[shashipoddar19]

Looking forward to replies. 

[muzaffer]

U80 is a gpio extender ie it generates an 8 bit register which can be read/write through I2C. It would be somewhat difficult to convert these gpio back to i2c. As your device is an i2c device, it would be easier to connect it to one of the outputs of the U44. Look at page 44 in ug850. There is a J59 which is connected to PMBUS i2c. If you are careful about address assignment you should be able to connect your device there.

Another option is to connect your device to J54 directly (check the voltage levels) and then generate I2c transactions by bitbanging the gpio. ie connect sda/sclk of your device to 2 pins on the connector (no pmod connector needed) and generate the correct bit patterns by writing to the gpio through i2c. This would be quite slow but possible.

[shashipoddar19]

Dear Muzaffer,

Thanks for your reply. I though had some queries associated with your previous replies and would be great to have your reply on the same. 

You have mentioned to connect i2c device to one of the outputs of U44. However, out of the available options most of them are connected to RTC/ HDMI/ IO expander without any option of feeding signal through any of them except PMBUS. We just wanted to confirm, if you referred the PMBUS_Data and PMBUS_CLK of J59 to be connectd to SDA and SCL of I2C device for interfacing the sensor directly. And, if there is an application note on the same! 

Another option to connect the device to J54 directly seems a mystery still. The pins of J54 are not directly addressable, and thus does not understand your proposed solution of bit-banging the GPIO. However, connecteing the I2C device through any other GPIO pin or an FMC pin might still seem to work out, though have not tried that. 

[muzaffer]

PMBUS_Data and PMBUS_CLK of J59 to be connectd to SDA and SCL of I2C device for interfacing the sensor directly

Yes, that what I meant. The TI parts are also connected the same way. and it's possible to execute i2c transactions against them. Once you find a suitable address for your sensor and program the switch to select pmbus, it is just like talking to a regular i2c device. I don't know an app note but the board user guide says somethings on this topic.

The pins of J54 are not directly addressable, and thus does not understand your proposed solution of bit-banging the GPIO.

The pins of the j54 are connected to a register the bits of which are controlled by an i2c slave. So you execute a byte write to an i2c address and the byte appears at j54 pins. As I have said, it would be quite slow and complicated as the direction of the pin connected to sda needs to be changed etc. but at a high abstraction level this can be treated like a byte gpio. If you can do byte gpio to control bits of the same to do i2c, this can be used for that method.

[shashipoddar19]

We tried connecting the PMBUS_Data and PMBUS_CLK of J59 with SDA and SCL of I2C but was unable to find any dedicated address provided for J59 in the guide provided. My sensor has an address of 0x6B as known while interfacing with micro-controller, but in order to connect it through J59, we need to select PMBUS compatible to address this sensor. 

So, could you please let us know how to select suitable address for J59, to connect a sensor!

[muzaffer]

I don't know to what table 1-19 refers. The pca9548 is just a switch so after you set channel 7 as the target by writing to its control register you should be able to talk to any i2c device on that channel which doesn't conflict with the existing ti chips on the same bus; and your sensor doesn't. Just try and see if it would work.