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[WP-34S] Cable and flashing options for Mac users
01-26-2015, 05:41 PM (This post was last modified: 01-27-2015 12:06 AM by John Galt.)
Post: #112
RE: [WP-34S] Cable and flashing options for Mac users
Some interesting timing measurements:

(first picture) Flashing the calculator sends many records of length 22 mS (upper trace). The required replies from the calculator (acknowledgements, lower trace, at the trigger point "T") occur approximately 9 mS after each record is sent - I think each and every record gets a reply, but I am not certain.

The entire file, most recent version takes 19 or 20 seconds to send from my Mac so the approximate total number of records can probably be derived from that.

(second picture) The reply (lower trace) consists of only a few bits but they're always the same, and of 78 uS in duration. It corresponds to ASCII character Y (upper case). Or, it's just a nice symmetrical character to choose - zero one zeeeero ooooone zero one stop :-)

I suppose N would represent a negative acknowledgement.

(third picture) The initial transmission from MySamBa. It corresponds very closely to 115200 bps and completely confirms Mr. von Cube's explanation of the protocol. Subsequent transmissions occur at exactly that same speed on my calculator, but it's unlikely that everyone else's will do that and MySamBa won't need to adjust transmission speed... however it does that.

If MySamBa receives no reply at all, it sends the exact same thing and at the exact same speed, a total of three transmissions before it gives up. This puzzles me, and I still wonder how it's supposed to cope with a calculator lacking a crystal timebase that might not recognize the bitrate.

(fourth picture) During normal communication, subsequent transmissions occur a minimum of 5 mS after the previous one's reply. Sometimes it's more than 5 mS.

With respect to Mr. Meheut's wp34sflash program, the reason it doesn't work is obvious. What it sends is completely different and bears no resemblance to what MySamBa sends. What it does, and what I have not been able to observe MySamba doing, is to vary the bitrate from the first transmission to the fourth (it sends four before giving up). The hard work in porting MySamBa's essential functions to the Mac is surely done though, and if he would be so kind to point me in the right direction for its source, perhaps I could make that program work.

If you don't have a scope, Mr. Jebem's Tx and Rx LEDs are VERY helpful diagnostic tools. They clearly show activity when it's supposed to occur. If the calculator is OFF (a bonehead mistake I've made more than once) the Rx LED will glow faintly but steadily, indicating something is wrong.

Maybe this information will help others if they have trouble, I suppose most people won't care.

On a related subject, it seems pretty difficult to kill the calculator. If I haven't fried something by now I probably never will :-p

I realize flash memory can only withstand a finite number of flash cycles (10,000 according to Mr. Bonin's manual, footnote 49). I'm two or three dozen into that, and will start counting! For this reason I am limiting testing to a sacrificial machine.

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RE: [WP-34S] Cable and flashing options for Mac users - John Galt - 01-26-2015 05:41 PM

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