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[WP-34S] Cable and flashing options for Mac users
01-22-2015, 06:59 PM
Post: #59
RE: [WP-34S] Cable and flashing options for Mac users
Thank you for the words of encouragement Barry, it means a lot to me.

I completely agree with you that there is something electrically wrong, but I am at a loss to determine what it might be.

I also agree the calculator is not totally dead, since powering it on causes about 8 mA to flow from the power supply (see the picture - to eliminate that concern I am no longer using batteries). Pressing the reset button through the hole in the back causes current to cease, and pressing ON again draws 8 mA. Therefore, the calc is "working" in that it responds to those inputs, but as far as I know once its firmware has been erased there are no other overt means of determining its operational state.

The electrical connections are so simple there is no need for a picture.

The Prolific USB cable presents four conductors:

Red (USB supplied 5V at 500 mA, which I am not using yet)
Black (signal and power ground)
Green (TTL Tx, to calc)
White (TTL Rx, from calc)

Black: connects to a center battery clip.
Green: goes to the upper leftmost programming pad, through a 1k resistor.
White: goes to the one to its right - the upper center programming pad, through a 1k resistor.

Power supply (an HP no less!) connects to the battery clips, which I understand are internally connected to one another in parallel. I verified that too.

MySamBa (the PC program) or wp34sflash (Mr. Meheut's OS X program) both send approximately the same signals. There are rather significant timing differences I could describe, but I don't think they're relevant quite yet.

About the $1.79 eBay cable I bought: as far as I can determine the cable and its drivers are doing everything they can be expected to do. A loopback test (using minicom as well as other utilities) performed by connecting Rx and Tx together is 100% successful: typed characters are echoed. Break that connection, and characters are not echoed. The signal levels are always well-defined, and the loopback test succeeds even if I impose significant noise and distortion in them.

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. Inductive coupling perhaps? One would think the calculator load should eliminate that concern. It's the same cable dewster used so I'm skeptical of inductive coupling.

Quote:One suggestion is that you use an ohmmeter to verify the connections and to verify that TX and RX are not coupled to each other in some way.

Yes, the resistance between them is infinite so the reason for the apparent signal coupling remains unknown. Both my cables do the same thing.

So yes, something is electrically wrong. I don't yet know what it is. The exact same cable worked for others though so I'm reluctant to blame it right away. If either serial line is broken in the HP30b internally though, I would see what I'm seeing.

Quote:Perhaps you can find someone in your area of the country to flash the WP-34S for you.

Someone was already kind enough to lend assistance so I think I'll take him up on the offer. Bear in mind my goal is not to flash the calculator and be done with it; I'm trying to find a solution for Mac users to do that on their own.

At the moment I need to (1) verify my Prolific USB cable works using otherwise proven hardware / software (PC, calc, MySamBa) and (2) verify my calculator isn't totally dead. If both of those uncertainties are eliminated, I'm back to troubleshooting my computing platform.

Your suggestions are quite welcome, thank you! This site is a terrific resource.
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RE: [WP-34S] Cable and flashing options for Mac users - John Galt - 01-22-2015 06:59 PM

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