Some time ago I tried to make the serial port shield for my Parallax Human Interface board. The Human Interface Board uses many of the Propeller's I/O pins for VGA, sound, mouse, keyboard and SD card. However it still leaves pins P0-P7, and they are available on a header on top of the board along with 5V, 3.3V and Ground pins. Originally I used transistor based circuit from Propeller manual which was recommended by Parallax for programming the chip via RS-232, but unfortunately it didn't work for me. I spend hours debugging, building the equivalent on a bread board, making modifications and experimenting, but all to no avail. Here is the circuit that didn't work for me:

This is how my shield looked like originally, inserted here on top of the Human Interface board:

After many hours lost trying to make it work, I gave up, tested a different much simpler circuit and de-soldered the components to make a new one:

This works just fine except occasional contact issues on the jumpers. I guess I need new jumpers because these are scavenged from some old board and seem to be loose and not making a good contact. I could have made permanent connections instead of reconfigurable jumpers, however I wanted to be able to re-configure hardware connections of Rx/Tx serial port pins to a different Propeller I/O pins if needed. I think this makes this simple shield much more practical.

My development system just got a little bit better.

After all that hard work, I fired up my MKHBC-8-R2 computer to have some fun playing BASIC game on my new shiny Propeller based terminal: