Magellan 315
There is a Great deal of information out there about GPS handheld receivers, but it can be hard to find useful info on a specific model, so as I own a Magellan GPS 315 handheld I've posted all the usefull info I know about it, for those of you who also own a 315.
If you want to make your own serial data cable here [PDF] is the link on how to do it. I built one without the +3.8v input and it works fine with my B2154. Once you've made your data cable go to the magellan website and you can download a firmware update.
If you don't have the user/ owner manual Magellan post it on their website here [PDF].