There is a mini ISA adapter that can adapt to the built-in expansion card slot of Pocket386,It uses 3f8h port and IRQ4 interrupt. Transmit TTL voltage serial signal through the common line on the back of the machine.

Schematic Diagram:

PT386-miniISA-COM1-Rev1.1.pdf

PCB file:

PT386-miniISA-COM1-Rev1.1.rar

The TTL-RS232 module can convert between TTL voltage and RS232 voltage

Schematic Diagram:

PTxx-TTL-RS232-Rev1.0.pdf

PCB file:

PTxx-TTL-RS232-Rev1.0.rar