This device fits into a usual plastic 9-pin D-Sub shell.
Of course, SMD devices are used heavily.
The power supply comes from serial port too
and is designed for maximum flexibility.
It uses all three output lines in both polarities
(6 diodes, looks like a three-phase bridge rectifier).
Even when all status lines are inactive, a toggling TxD line
will be sufficient as power supply.
Moreover, control and status lines are connected for built-in
“hardware-handshake” for RTS+CTS, DTR+DSR, or both usual interlock systems.
This PCB is designed for professional manufactoring.