Odd factory mod on TRS-80 26-3612 (Sharp CE-158) RS232 interface

[Chr Yoko]

Looks like that RS232C interface is common between PC1500 and PC1600.
But as the PC interface wiring is different between the 1500 and 1600 (2 pins are inverted if my memory is still ok). So there should be some kind of circuitry to switch between both.

If interested i can share some USB-PC1500/1600 interface circuit design.
You can find some designs onto Sharp Forums.
There are even BlueTooth interfaces circuits available now.