Serial cable for WP-34S : few questions

[Francois Lanciault]

Hi,

I am building my own serial cable for the WP-34S and I have a few question:

I know the ERASE button should short the +3V pad and the erase pad. What about the reset button? For what I could deduced it needs to short the reset pad with the ground pad. Can someone confirm ?

The Tx pad means Tx at calculator level and should be connected to the Rx pin of the host computer. True ?

Same for the Rx pad on the calculator; should be connected to the Tx pin on the computer ?

Thank you!

François

[Marcus von Cube]

(02-08-2015 04:49 PM)Francois Lanciault Wrote:  I know the ERASE button should short the +3V pad and the erase pad. What about the reset button? For what I could deduced it needs to short the reset pad with the ground pad. Can someone confirm ?

I can confirm.

(02-08-2015 04:49 PM)Francois Lanciault Wrote:  The Tx pad means Tx at calculator level and should be connected to the Rx pin of the host computer. True ?

Same for the Rx pad on the calculator; should be connected to the Tx pin on the computer ?

Also confirmed! Be aware that the voltage level is 0-3V, not RSR232 level! The latter can kill your calculator. An FTDI USB converter chip will do nicely.

[Francois Lanciault]

(02-08-2015 05:20 PM)Marcus von Cube Wrote:  Also confirmed! Be aware that the voltage level is 0-3V, not RSR232 level! The latter can kill your calculator. An FTDI USB converter chip will do nicely.

Thank you for this information! I was just about to plug everything directly to the RS-232 port of an old PC. So I guess the "official cable" was doing the conversion from +/- 12V to the 0-3V required.

I think I have a converter from RS-232 to TTL level. Does 0-5V would do or it really needs to be 0-3V max ?

François

[Francois Lanciault]

(02-08-2015 06:19 PM)Francois Lanciault Wrote:  

(02-08-2015 05:20 PM)Marcus von Cube Wrote:  Also confirmed! Be aware that the voltage level is 0-3V, not RSR232 level! The latter can kill your calculator. An FTDI USB converter chip will do nicely.

Thank you for this information! I was just about to plug everything directly to the RS-232 port of an old PC. So I guess the "official cable" was doing the conversion from +/- 12V to the 0-3V required.

I think I have a converter from RS-232 to TTL level. Does 0-5V would do or it really needs to be 0-3V max ?

François

I think it is going to be ok. I have this converter:

https://www.sparkfun.com/products/8780

And I can decide what voltage it will output so I will use 3V volts.

Thanks again.

François

[John Galt]

If you don't plan on erasing your calculator repeatedly, an inexpensive (commonly available for less than $5 USD) USB to serial converter cable is all that is required. Search for a description resembling "Prolific PL2303HX USB To RS232 TTL USB To COM Serial Adapter Cable". That, and a suitable current limiting resistor for each of the Tx and Rx lines. I use 1 KOhm.

Even if you erase it, doing so is a simple matter of connecting the Erase pad to power while turning it on. The erase procedure, adapted from p. 167 of the WP 34S printed Owner's Manual, is as follows:

1. Switch calc off or press RESET in back to turn it off.
2. Connect Erase (J36, lower left) to Vcc (J31, upper right) and leave it connected until Step 5.
3. Press ON. Calculator will turn on and the display will be on.
4. Press RESET. Calculator will turn off and the display will be off.
5. Disconnect the jumper in Step 2
6. Press ON. Calc will look dead but it is really ON and drawing power.

You are now ready to flash the calculator using the MySamBa Windows program. If you are not ready to do that yet, pressing the RESET button will turn the calculator off so that it does not continue to deplete the batteries. Press ON when you are ready to flash.

The reason for initially stating "if you don't plan on erasing your calculator repeatedly" is that once an HP 30b has been converted to a WP 34S, updating its software does not require erasing it again. That procedure is described on p. 171 of the printed manual, and only requires connecting the Tx and Rx pads and signal ground. You can easily hold those three conductors in your fingers, or just two conductors if you remove one battery and connect signal ground to the battery center conductor which is also ground.

The calculator's onboard power is perfectly adequate for flashing, provided the batteries are relatively fresh. Flashing draws considerably less current than running some programs, and it takes about 20 seconds.

Press RESET after MySamBa reports the file was successfully sent, then, disconnect your programming connections, replace the battery if you removed one, and press ON.

The above was adapted from several sources who contribute to this site.

Edit to add picture below.

• There is one 1/4 W 1 KOhm resistor inside each of the green and white shrink tubes.
• The ribbon cable to the left ends at a connector I fabricated, but it's optional.
• The bare Vcc (J31) and Erase (J36) conductors on it are used for the erase procedure.
• Hidden behind the signal ground (J34) conductor is the Reset (J32) conductor, but it is not required since grounding it is identical to pressing Reset on the back of the calculator.
• The black cable to the right ends at the Prolific USB to serial converter that plugs into your computer.

So all you really need are three conductors.

If you are observant you will note the green and white shrink tubes do not agree with the green and white cable conductors of the cable. That's because the cable I bought did not agree with its documentation, so be sure to verify yours.