WARNING: I am not responsible of any damage, harm or pain caused by using this information under any circumstances.
WARNING: I am a human and make mistakes as other people do, so check connections before power-on. Feel free to send me notes and comments.

NOTE: Default serial port settings for Corel Netwinder is 115200 8N1.

This page describes a solution for Netwinder without usual daughterboard. Corel used Winbond W83977AF chip as a Super-IO. As a voltage transducer I have used MAX232, which is commonly used worldwide. It's usage was directly taken from datasheet. I transformed only needed signals - RxD and TxD for two ports. So, if you need others (RTS/CTS, DSR/DTR etc) you would need to use more transducers.

Port A (ttyS0) is normally located on daughterboard, but port B (ttyS1) is hidden from outside and as I know used only in rackmount version of Netwinder. As you can see in W83977AF datasheet this SuperIO has first two ports on pins:
53 - Serial B TxD
54 - Serial B RxD
46 - Serial A TxD
45 - Serial A RxD

This figure shows needed pin locations on daughterboard.

Connectors locations

Serial B connector is pin-pin compliant to PC DB9 serial port. Pinout:
2 - TxD
3 - RxD
5 - GND

Next figure shows connector used for power and Serial A.

Connector pinouts

Last figure shows full schematic made. If you use MAX232 capacitors C1-C5 should be 1 uF. In case of MAX232A they should be 0.1 uF.

Schematic

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