Handspring Visor


Senior Member
Any suggestions for interfacing a PICAXE to a Handspring Visor using the serial port? The Visor uses TTL levels.



Senior Member
Do you have a terminal program installed ? There are apparently heaps of them for Palm OS => www.pilotzone.com/palm/comm_term_default.html.

Picaxe RS-232 levels are usually OK on most TTL PDAs I've tried. See a Casio PV at work => www.picaxe.orcon.net.nz/pvdemo.jpg Stan


Technical Support
Staff member
One man's TTL can be another man's accident waiting to happen.

Page 71 of http://www.splorp.com/pdf/handspringdevkit.pdf suggests that 'TTL' may be 3.0V, which could require some precautions.

Does the question relate to physical or electrical connection, protocol or software issues ?

What prior experience do you have regarding Handspring, PICAXE, and serial interfacing ?


New Member
I've had some experience using TTL level devices with a Palm device and with PICs. I suspect the issues with a Handspring are similar,due to the incestuous nature of the two design teams. The Handspring folks were formerly Palm people.

In practice, most modern RS232 switches at around a volt, not zero volts, so that +-12v RS232, +-5v. RS232, and TTL devices can be interfaced.
Any well designed serial device should have protection from +-12v. on its RX line , though maybe not on its TX line, leaving that to the receiving device. Put in a 22K resistor to limit current and a diode to block the negative voltages on the Picaxe RX line and you will protect against even +-12v signals, just like the Picaxe Programming interface does. If you are really paranoid, put in a 220 ohm resistor on the TX line as well.