[WP-34S] Cable and flashing options for Mac users

[jebem]

(01-23-2015 01:38 PM)John Galt Wrote:  There is no guarantee that the USB shell might always be so easily disassembled though, and a simple loopback test is insufficient to identify reversed Tx / Rx conductors. Could you use a diode to identify the proper conductors?

Hi, John,
Thanks again for your dedication on this project. Really appreciate, as I have learn a couple of things, specially concerning your specific Mac environment.
And let's not forget your excellent work on the POGO connector (and thanks to Dave for the additional hints!).

Concerning the method to discover the USB-Serial adapter TxD wire, I would just connect both TxD and RxD wires to the GND wire using a 1Kohm resistor on each one.
Then I would send a stream of data and use a oscilloscope to read the signal.
The wire with a signal is the TxD from the USB adapter.
The RxD should not show any significant signal in these conditions.

I didn't test it myself, but I can do it during the weekend if needed.

EDIT:

On second reading of your post:
Did you mean a LED diode connected between the TXD wire candidate and GND to find out which wire is send a data stream?
Now, that seems to be a nice idea!
Because the maximum source voltage is 3.3V and a small LED diode takes at least, say, 5mA to light up, we should use a 220R limiting resistor (220 ohm) in series with the LED diode.
The only doubt is related to the maximum available current from the TXD drive circuit. If you look to my schematics, I use a transistor buffer to drive my LED diodes, and in this way I'm not overloading the Prolific driver circuits.
But it is worth a try.