The cable to the wp 34s


Hello, when I googled RPN calculators i found the threads in this forum about the wp 34s. The idea with a updateable scientific calculator with rpn in 42s style is interesting. As I have an hp 20b I thought I should try your firmware.
My problem is the cable. My questions is if I can use an UB232R module with ftdi chip and datasheet
As I understand it i need to sett the reset and erase
line high manually some times in the flash process so I need two a (debounced?) button to do this. I found some threads with information about use a ftdi ship to get serial communication. Do this solutions works to flash the unit also, or is it necessary with some solution to set reset and erase high to use this solutions to the flashing procedure?


Hallo Josef,

Your questions are answered in the manual, top of page 5 and on page 110. Happy reading :-)


Josef, one of my units brings out the three lines rxd, txd, and gnd to a 2mm stereo jack, borrowed from a TI "black" cable. You will need the 3.3V cable from FTDI, it should work out of the box.

RESET is no problem, the calculator has a hidden button on the back under a hole near the special connector and the batteries. For ERASE, you need to connect the erase bin on the connector to the 3V supply while the processor is doing something. You can force this by pressing and holding the ON key which will forcibly wake up the processor. If you need them I can send you the schematics of the 20b from the SDK. It's the same for the 30b.

If you open the calculator, add the crystal and its two caps as well as the IR diode and resistor. You will not regret it if you can get hold of an IR printer from HP. :-)


Thanks you for your answers. (both of you)
I think I found the schematic of the 20b in the sdk from the wiki link. I try to do the other modifications also. Thanks :)

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