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Original question:

UART to I2C Bridge

I2C to I2C bridge with opto-isolation

Frank Eory2
Prodigy 200 points
Other Parts Discussed in Thread: ISO1640, ISO1412, ISO1044, P82B96, ISO1641, ISO1540, ISO1540-Q1, ISO1541, ISO1541-Q1

Hello,

We have a product made up of one master unit connected by a cable to another slave unit. The communication is only I2C. The slave unit only has I2C peripherals with no CPU. The master has a CPU. The management likes me to use an optical cable (with as little quantity of fibers as possible) to have full isolation.

Do you have a solution to convert master side I2C to serial  and to convert serial to I2C without any new software that needs to be developed?  The closest I found is slaa908   (UART-to-I2C Bridge Using Low-Memory MSP430Tm MCUs) that does serial to I2C only.

The sloaa908 assumes the CPU is talking to the the serial side. This means in our master unit, we need to get the software person to rewrite the software to make all the code now talk to a new serial port. I would run the 2 optical lines to the slave unit. In the slave, I would have to add the MSP430F2311.

 

 Or do you have any different ideas that involves no software?

Thanks,

  • 0
    TI__Guru 53115 points

    Hi Frank,

    Thanks for reaching out.

    TI does not provide any fiber optic communication transceiver solution but we do have I2C isolators that can work well. The ISO1640 is I2C isolator which accepts I2C signals on one side and isolates them onto the other side. This doesn't require any software overhead, the isolator is transparent to the whole system. Please do take a look at the ISO1640 datasheet and let us know if this meets your requirement.

    Please do note that the I2C communication lines are good for short distance communication, preferably between devices on the same PCB or between PCBs that are located very close by. If you meant to connect two units that are locate very far from each other, then I2C as is might not work and, like you mentioned, you may require conversion of I2C into some other interface.

    I would also like to mention that the two popular interfaces for longer distance communication are the RS-485 (example device: ISO1412) and CAN (ISO1044). Let me know if this is of your interest, thanks.


    Regards,
    Koteshwar Rao

  • 0
    Guru 272400 points

    I²C already is a serial protocol. What makes it special is that the signals are bidirectional. If you really wanted to use optical signals, you would need to use a P82B96 on each side to get unidirectional signals, and then add optical transmitters and receivers to the Tx/Rx/Ty/Ry pins.

  • 0 in reply to Clemens Ladisch
    Prodigy 200 points

    Hello Koteshwar and Clemens,

    Thanks for your response. ISO1640 and ISO1640 are not stocked now. Koteshwar, can you propose some other chips? Clemens came up with P82B96. I could put galvanic isolation in series with that, unless you have another et of chip in mind.

    This I2C over long cable was designed by somebody else. I got an email from one manager that is not an EE saying to go all fiber, with the email carbon copied to all of management. The company I work at does laser equipment, so management tends to like optics. I do intend to propose wired solutions with wired serial differential. I never designed with RS-485 before. I did do before LVDS over cables.

    Thanks to both of you.

  • 0 in reply to Frank Eory2
    TI__Guru 53115 points

    Hi Frank,

    Thanks for your response.

    The isolated I2C devices that we currently have in our portfolio are ISO1640, ISO1641, ISO1540, ISO1541, ISO1540-Q1 and ISO1541-Q1. I understand the stock might not be available all the time due to current high demand but please note that these stock get filled and parts become available. Please subscribe by clicking "notify me when available" option on the ordering page so that you get notified when the parts become available. Thanks.


    Regards,
    Koteshwar Rao