Following the information in SC16IS752 and in MAX232, I'm attempting to make 2 Arduinos communicate with each other over RS232 (because of the distance it can get compared to other protocols) and using the I2C to 2 UART so that several UARTs can exist at the same time.
I've attached the schematic I've used for each side.
In addition, I've tried just getting the SC chip to talk to another and had success, and I've had an Atmega328p using the MAX232 on its hardware serial port talking to a desktop. Neither of these were a problem, but when trying to get 2 Arduinos communicating over the I2C to RS232 or even just getting one Arduino to talk to a desktop, it doesn't work.
In the next post I'll upload the code for the Arduino.
When the Arduino communicates to the computer, I see 0xFF on the computer side and 0x00 on the Arduino side.