The PIC microcontrollers have a UART with a TX and RX.
You can connect TX on one chip to RX on another chip.
I was reading about SIMPLEX and DUPLEX.
You can connect TX on one chip to RX on another chip.
This is SIMPLEX.
The TX transmits and RX receives.
If you had Chip A and Chip B you could wire
A.TX to B.RX B.TX to A.RX
The simple microcontrollers have a UART with a TX and RX. They support 5,7,8 and sometimes 9 bits.
5 bits for BAUDOT 7 bits + Parity 8 bits 9 bits , where the 9 bit indicates ADDRESS
The UART from 40 years ago did not support the 9 bit.
If you are sending 8 bit characters with the UART set to 8 bits, there is no spare bit for a second channel.
I had an idea.
If RS-232 serial had an extra bit it could be used to handshake.
RS-232 has the extra wires RTS, and CTS
Unfortunately UARTS do not have spare bits.