In SX Microcontrollers, SX/B Compiler and SX-Key Tool, Jon Williams wrote:

Well, according to the USB2SER docs (hint, hint), the red led should light when data is being received on the TX line (I know this seems backwards, but it is correct) and the green light when data is coming from the RX line -- that happens on my setup.  After looking at the schematic I think your adapter should have been saved by its design: there are 1K resistors in the TX and RX line.  The RES line got connected to the OSC1 pin on your SX, and as it goes to the collector of a transistor I doubt any damage was caused.

I used the attached program to suss everything out.  Run the program with these connections to your USB2SER:

RA.0 ----- TX
RA.1 ----- RX
 Vss ----- Vss

The program starts with a loop that just receives.  Fire up Hyperterminal, select the comm port assigned to your USB2SER, then open the connection -- you should have to press a key 10 times (the red LED will light with each keypress).  After that, when you press a key the SX will echo it back with a little ">> " prefix -- the green LED will light when this happens.  Note that at 115200 the LEDs are on nearly simultaneously.

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