Posts: 102
Threads: 3
Joined: Sep 2007
Quote:
So Gene, what is it about these cables that makes them unique from any Serial/JTAG cable? Is it just the two buttons?
If so is there a procedural workaround where the buttons would not be necessary? Or a simple mod to add switches to another cable.
I'm thinking about when you do run out. But also considering the idea Marcos posted earlier where he soldered in a small stereo audio jack (Tx, Rx, Gnd only). With this set up, a cable like those used to program the PICAXE would work (like the AXE027).
The two buttons (ERASE and RESET) are needed to get into the bootloader on the calc in order to flash the new firmware.
The HP cable is a 3v to RS232 level shifter, plus the two buttons. It uses six pogo pins to connect to the calculator (2x3 pads underneath the battery cover).
In "Interfacing to the HP20b V3.pdf" Richard Nelson shows some good close up pictures of the guts of the cable. I think there is enough detail you could wire up your own two buttons on any common level shifter. Then you just need the pogo pins or reasonable facsimile thereof.