Well its bit of challenge for Jerome to teach me how to do a Mainframe on a PI with serial terminal. I started the project using a old HPE 700/96 terminal amber. I used this site as my prime info.

https://www.cyberciti.biz/hardware/5-linux-unix-commands-for-connecting-to-the-serial-console/

First is seeing if you have a serial port

dmesg | egrep --color 'serial|ttyS'

Then install getty if its not there

Then add your config line to /etc/gettydefs

Then make work if you reboot.

The do report

Then you have the log in prompt on the terminal