Registered: Dec 1999
Location: Connecticut USA
Posts: 2682

Many questions have been raised about the capabilities of the Visor's serial port. I think this has confused many people who thought they could just connect to serial devices with a cable.

I have received some information direct from Handspring Deveploper Support and thought I would pass it along.

First off, the Visor serial connection requires a transceiver circuit to change the TTL-level Visor signals to RS232-level. This circuit needs to be powered by an external source... the Visor CANNOT drive it. On a PC connection, power can be derived from the serial port but most peripherals (i.e. modems) DO NOT provide the "parasitic" power to drive the transceiver. This HAS been confirmed to me by Handspring.

From a software point of view, typical serial communication applications, when run on a Visor, DO NOT use the serial connection. They are routed out to the Springboard slot where they expect to find the serial device. Handspring tweaked the OS in this area to allow for the use of USB. This as well HAS been confirmed by Handspring.

Below is an except from the email I received from HSDevSupport:

quote:

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Serial Port:

As for a "generic" serial cable for the Visor, note that there are some differences between the Visor and other devices from Palm Computing in terms of the serial connection. Also note that USB is available on the connector as well (the Visor is a peripheral USB device).

The Visor has serial as well as USB on the "cradle" connector (at the bottom of the Visor). However, there are only two contacts on the connector for serial communication (TXD and RXD) in addition to a GND connection. Also note that these signals are logic levels based on a 3.3 volt system, not true RS-232 levels. The TXD and RXD signals are buffered with a part running at 3.3 volts, but these parts are 5 volt tolerant. The optional serial cradle that Handspring offers actually has a level-shifter built into on the cradle to make sure that it works with a serial connection on the computer.

There are also several serial handshaking signals that are present on Palm cradles that AREN'T present on the Visor cradle. It will therefore depend on what the device that you are connecting to requires in terms of handshaking, signal levels, etc. as to how to best make it work electrically. The Handspring Developers Kit Manual suggests that asynchronous serial communication over the serial port (without hardware handshaking) is limited to 9,600 Kbps or less, but you may see better performance than this if you experiment.

In terms of communication over the serial port, I have successfully communicated from my Visor (via a simple terminal emulator) over a Visor serial cradle to a Mac running Zterm (a terminal emulation program). We have also successfully communicated over the serial port (via a Visor serial cradle) in doing source level debugging via CodeWarrior.

To get detailed information about the Visor serial connection/cradle, check out:
http://www.handspring.com/developers/developers_kit.asp

Download the Developers Kit Manual (DkManual.pdf) from this page. Section III (in particular) has some information about the pinout of the cradle connector, including the serial section.

To have something to compare it to, you can get detailed information about the Palm serial connection/cradle at:
http://www.palm.com/devzone/hw.html

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Registered: Jan 2000
Location:
Posts: 434

Thanks, Mark! So. How do you redirect an apps serial comm session to the cradle connectors without rewriting the app? I'm guessing that it can't be done without a rewrite?

Registered: Dec 1999
Location: Connecticut USA
Posts: 2682

quote:

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Originally posted by yucca:
I'm guessing that it can't be done without a rewrite?

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code:

 * FileName:
 *		UsbLib.h
 *
 * Description:
 *		This file contains functions for the USB Library 
 *    that replaces the Palm Serial Library.  This library is API
 *    compatible with the Serial Library.

Registered: Jan 2000
Location:
Posts: 434

Hmmm. This is not promising, I guess I had better get that efig serial module if I want a real serial port . . .