Digital interface SPI/I2C

[engr_joni_ee]

We have FPGA development custom board in our project and also we have another board (let's call it board A) on which there are some chips having I2C interface. The FPGA board is supposed to communicate to the board A through I2C in order to talk to the chips on board A.

We need to add one DAC on board A and we have chosen for some particular reason MAX5541 but this chip has SPI serial input. Do we need another "set of wires" for MAX5541 on board A so that FPGA board can communicate to it ? Can we use the same two wires of the I2C on the board A that is shared with some chips on board A to communicate with MAX5541 ?

Here is the datasheet of MAX5541.

https://www.analog.com/media/en/technical-documentation/data-sheets/MAX5541.pdf?ADICID=SYND_WW_P682800_PF-spglobal

 

[KlausST]

Can we use the same two wires of the I2C on the board A that is shared with some chips on board A to communicate with MAX5541 ?

What´s your idea? I2C works with 2 signals, while SPI works with at least 3 signals. Where does the third signal come from?

You may see I2C and SPI as two different languages.
So while you are free to generate your own "interface translator". But both interfaces have rather different ways to communicate, different addressing, different timing...
Thus you need to spend some time to define "your own rules" for your translater. And then need write the code for it, both on your I2C master and your translater (FPGA).

****
We don´t know why you did chose the I2C interface, nor why you chose the SPI device .... So in the end its hard to give good advice.

Klaus

 

[barry]

The short answer is you can’t run SPI and I2C on same bus.

 

[engr_joni_ee]

I found this device NXP SC18IS606PWJ which act as I2C to SPI converter/bridge. I was looking for such device.

Now the FPGA board will communicate through I2C with NXP SC18IS606PWJ physically located on the Board A together with other I2C devices. The FPGA will act as I2C master and the NXP SC18IS606PWJ will be I2C slave on the Board A. The NXP SC18IS606PWJ have SPI interface on the other end which will be connected to DAC MAX5541.

https://www.farnell.com/datasheets/3685598.pdf

The problem was that we could not add more wires between FPGA main board and the board A.

 

[KlausST]

Hi,

informations we got now, but missed in post#1
* "I was looking for such device."
* "The FPGA will act as I2C master"
* "we could not add more wires"

You asked: "Can we use the same two wires of the I2C"
Thus I thought: (I2C) SCL, SDA ---> directly connected to --> MAX5541 ... which does not work.

Thus also I asked questions in post#2 ... but you never answered.

****
In either case ... we often ask for a skech ... for a good reason.
I wouldn´t be surprised that some user recommended an IC like you use now ... but three weeks earlier.

So in the end ... there was an avoidable delay of weeks... for you / your project.

Klaus