HP produced two serial I/O interfaces for the 9830. One was a minimal-hardware bit-banged interface requiring a special option-ROM. The other contained more logic, doing the serialisation in hardware.

This is a new (2024) RS232 Serial I/O interface using a UART. The device select code is switch configurable. With the select code set to 15, the interface can function as the primary printer for listings and print output.

Resources: RS232 Serial Schematic (PDF)