Thank you for ideas.

The MCUs are on same board and has your serials are occupied. I am using P89C51Rx2 that hasn´t I2C bus.

I will try to use one MCU that has I2C or additional serial, but I think now its impossible (The delivery time on Brazil unfortunately is about one month).

So, the solution is to put the link using some kind of serial interrupt driven communication as explained on my first post.

Best Regards

Jean Fernandes
Electronic Engineer
Brazil