making HP39GS Serial Cable (RS-232)

[ilkka777]

(05-02-2019 09:14 PM)rprosperi Wrote:  You are asking the SERIAL port and not the USB port, right? (it has both)

Assuming you mean the serial port, see notes on this page:

https://commerce.hpcalc.org/serialcable.php

This is about the 50g, but the serial port in the 39gs is the same h/w as the 50g.

Also, more details here:

https://www.allenwan.com/hpcalcserialcable/

I wonder what is the protocol used? looks like to be full duplex, and not right rs-232. RTS and CTS signals looks like to be used. Receiver pulls its TX line up (CTS? send as RX for sender) and sender pulls its TX line up (RTS?), maybe I got signal level problem since I cant get HP39GS (around 5V Vcc) sending anything to my arduino (3.3V). I dont understand what is wrong?

I found this one for HP48, gives a hint that perhaps some kind of "proportional negative voltage levels" are used (?): https://www.keesvandersanden.nl/calculat...System.pdf