Palm PDA Cables

The Connected Organizer

Palm has long touted their Palm PDA devices as connected organizers. Other than add on devices for wireless data and infrared connectivity, the humble serial port is the key to connecting your Palm to the outside world. The Palm III series of PDAs have two different types of "free standing" cables available to it, the hotsync cable and the modem cable. What is a "free standing" cable you might ask? Well, it is just a cable without a cradle to support your Palm. However, when the Palm V came out, Palm decided to make only the hotsync cable and omit the modem cable. Furthermore, they no longer sold the hotsync cable separately (like for the Palm III), you had to buy the Travel Kit to get a "free standing" hotsync cable. This made life a little inconvenient (and more expensive) for the many Palm V owners.

Crossdress? Crossover?

Your telephone is a "bi-directional" communication device (communication in both directions). Serial cables however, as the name suggests, allows communication in only one direction. The little wires inside a serial cable transfer data from one source (the Transmitter) to a destination (the Receiver). On any device (PC, Palm, Printer), a fixed set of pin-outs is defined and all devices follow this standard pin-out scheme for the serial cable to connect to.

Let us take an example. Imagine if your PC had a serial port with two pins, pin 1 and pin 2, and your Palm has the same. They both follow the same pin-out scheme (since they are both serial ports) and have defined pin 1 as transmit and pin 2 as recieve. Serial cables connect pin 1 from PC to pin 1 on Palm and pin 2 from PC to pin 2 on Palm. A normal serial cable is therefore called a "straight" cable. Obviously, if you want to do bi-directional communication this is not going to work, therefore, you need to connect pin 1 on the PC to pin 2 on the Palm and vice-versa for the other wire. As you can see, this process is crossing one wire over the other one, hence the term "crossover". Such crossover serial cables are called Null Modem Cables. There are also Null Modem Adapters, that convert a normal (straight) serial cable into a crossover one. Of course this explanation is an overly simplified one, seeing as how a real serial cable has between nine and 25 pins!

In order for your PC to synchronise with your Palm, you need bi-directional communication. As such, your hotsync cable is (you guessed it) a crossover cable from the start. Here’s where the neat trick comes in. In order to access other devices that expect straight serial cables (instead of crossover ones), all you need to do is plug in a null modem adapter and wah-lah - you have a straight serial cable.

Getting such an adapter is actually quite easy. You can build one yourself if you know the proper pin-outs and have the equipment and supplies. Alternatively, you can ask a friend who can build one for you. Or you can get a shop to make it for you. I got mine from Fast Cable on the 5th Floor of Funan Centre. What you need to tell them is to make you a 9pin Male to 25pin Male Null Modem Adapter. You can also make a 9pin Male to 9pin Male Null Modem Adapter. Each adapter cost me S$5 and they made it for me on the spot in less than 15 minutes.

What do I want to do today?

The most common use for such an adapter is to connect your Palm to an external modem. Rather than buying the expensive Palm V Modem, you could get the 9pin Male to 25pin Male null modem adapter, plug it into your hotsync cable (or hotsync cradle) and your external modem and start surfing the web. Palm’s Modem Cable for Palm III is essentially the same thing but of course in a nicer looking package.

Another option is to print through a printer’s serial port. Some printers have a serial port (in addition to a parallel port) and as such may be configured to accept print requests through there. For example, I have a HP LaserJet 4000N (which has a serial port) and PalmPrint 2.2 on my Palm V. By hooking up a 9pin Male to 9pin Male null modem adapter to my hotsync cable, I was able to print using the software directly (in postscript even!) to the HP LaserJet. Okay, so IR would have been an easier option for printing, but not many printers support infrared printing as yet.

For those (like me) in the networking industry (or other such technology fields) you often come across equipment with Serial/Console Management Ports. These ports are essentially serial ports, but allow you to access the device’s management software. Some of them require crossover serial cables (ie. 3Com SuperStack switches), while others make do with straight serial cables (ie. Xylan’s OmniSwitch chasis switches). Having the 9pin Male to 9pin Male (and 25pin Male) null modem adapter together with your Palm and hotsync cable ensures that you can access any device’s management console anywhere. You might never need to carry that bulky laptop with you onsite anymore :) I’ve done so with both the 3Com SuperStack and Xylan Omniswitch using this technique and Palm Telnet 0.52.

And of course, it’s really cool to see your Linux server’s login screen in Palm Telnet when you hook it up to your server’s serial port. Actually, because you need bi-directional communication, you don’t need a null modem adapter for this trick, your hotsync cable (which is already a crossover cable) will do just fine. Just run a getty on /dev/cua0, open Palm Telnet, hit enter a couple of times and you’re in!

The caveat is of course that if you run overclocking software or such, you must make sure your software puts your Palm back to normal speed otherwise it will not communicate over the serial device properly. Also, since the Palm only has one serial port, it can’t be shared. While Landware’s GoType keyboard has a hotsync port on its back, you can’t type and connect to a modem at the same time becuase the GoType is already using the serial port to transfer your key presses. The new Stowaway doesn’t have a hotsync port on its back (why would you want one on a Stowaway anyway?). You should also set both the Palm and the other device to the same serial baud speed as well as the other usual 8-N-1/etc configurations for serial communications. 9600 baud and 8bit, No stop bit, 1 parity bit are very common serial communications settings. Palm OS 3.3 also allows you to move up to faster serial baud speeds, but from past experience, it’s not worth too much effort since the reliability of communications drops as you push the serial communications speeds up. Do also watch out for modem initialisation strings in your Palm. Refer to your modem manuals for more information on this.

Conclusion

In conclusion, the humble hotsync (and modem cable) is much more than just a cable to synchronise data between PC and Palm. Long before infrared, Bluetooth and wireless data, there was the serial cable. New applications based on this simple technology includes a demonstration of up to 4 frames per second of live video from a PC based web cam displayed on your Palm in Hong Kong. So, give the hotsync cable another look and it may turn your Palm PDA into a more connected organiser than you thought possible :)

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