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[WP-34S] Cable and flashing options for Mac users
01-22-2015, 10:43 PM
Post: #63
RE: [WP-34S] Cable and flashing options for Mac users
(01-22-2015 06:59 PM)John Galt Wrote:  I completely agree with you that there is something electrically wrong (...)

The Prolific USB cable (...)
Black (signal and power ground)
Green (TTL Tx, to calc)
White (TTL Rx, from calc)

However, the interesting thing about that cable is this: the scope picture I posted shows approximately the same signals even if I remove the cable from the calculator. In other words, the signal appearing on the Rx line is there even if I leave it open circuit.

Hi again, John,
Great effort and nice project of yours.

If I understood your test results:
- The USB-to-TTL-Serial cable works fine, as tested in loopback mode;
- The software tool to upload the firmware looks fine as well;
- The calculator can power ON, confirmed by an increase in current consumption.

Here is what I believe it is happening, and you sad it all:
- It is normal to see some signal cross-talking on the scope when you remove the cable from the calculator: This is caused by capacitive coupling on the cable and a high impedance on the Rx input circuit;
- The RX line must be loaded by the calculator output driver circuits, imposing a low impedance on the connection.
- So, as you say, it doesn't matter whether the cable is connected or not to the calculator - the result is the same. And why?
Most probable cause: The RX connector pin is not making contact with the calculator PCB pad, even if it seems to be making contact.
I would check it it a continuity meter.

Please share your results with us - Great job!

Jose Mesquita member

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RE: [WP-34S] Cable and flashing options for Mac users - jebem - 01-22-2015 10:43 PM

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