Frequently Asked Questions (FAQ) on Hardware

FAQ Index

Serial Problems: GPSyTM isn't seeing any data from the GPS

First of all, GPSyTM accesses the serial ports like any other communications application. There are some basic things to check:

Most importantly: Can, Zterm, Microphone, or any other communications program see your NMEA data coming in when set to the standard NMEA 4800bps; 1 stop bit; no parity setting? If other applications can't see the NMEA data, then GPSyTM can't either. If no data is coming into your Macintosh, then you need to triple check your cable and GPS setup. 99.999% of the questions we get regarding problems with GPSyTM and new configurations are due to problems with the data cable or GPS settings. Since these aren't bugs or defects in GPSyTM (and because GPSyTM hasn't implemented the electronic telepathy method of getting data from GPS units), they are extremely hard for us to "debug." So please verify through a telecommunications program whether or not you are receiving GPS data.

Note that serial ports vary in their sensitivity. So your GPS may work with a homebrew cable on your desktop but not work properly on your laptop or co-worker's machine -- especially if Pin 8 is shorted to ground. [We get the bizarrest accusations of copy protection because of this phenomena...] Be sure to read the Appendix on cable configurations in Getting Started carefully. For this reason, it's often safest to go with a pre-made, pre-tested cable.

Problems with bidirectional protocols (Garmin/Eagle/Magellan)

If you can get data successfully using the NMEA-0183 protocol, but have trouble using the Garmin, Eagle, or Magellan protocols, it's often because your data cable is only unidirectional (from your GPS to your Mac) and doesn't have the transmit line set up from your Mac to your GPS. This will cause all of the bidirectional protocols to failure (Eagle/Lowrance, Garmin, Magellan, Rockwell, etc.) while NMEA-0183 will work fine with just a receive line.

Global Mapping Systems provides a "it just works" guarantee for our own data cables however we unfortunately cannot provide support for user-constructed or third-party data cables since we have no control over how they are constructed. We suggest re-reading Appendix A in our documentation which covers cable issues extensively and contacting your cable vendor and GPS vendor to ensure you have a properly constructed, bi-directional data cable.

If your Garmin uploads and downloads work, but you're experiencing problems using the "Garmin real-time positional protocol", this may be due to instabilities in the Garmin real-time protocol mode. We suggest using NMEA-0183 whenever possible for navigation since NMEA-0183 is more stable and provides much more information than the Garmin real-time mode.

What about Bluetooth GPS units?

We're pleased to have added support for Bluetooth GPS units in GPSy X 3.40. We are currently only support GPS units that register as serial devices. This includes most of the smaller generic Bluetooth GPS units as well as a limited number of handheld units. Unfortunately, some Garmin and other handheld units are not registering as serial devices but are using a proprietary protocol. We are working to support these units and hope to announce this feature shortly.

Can I use my Palm Pilot adaptor as a generic GPS adaptor?

Several customers have written in to ask if they can use their Palm Pilot DB-9 to MiniDin 8 Mac adaptor to hook their GPS units up to their Macs. Similar adaptors are also found bundled with some digital cameras. On the surface, they look very similar to our "Generic PC Adaptor" and people want to know if they should shell out the extra money for our cable.
Palm Pilot Adaptor GPSy Generic Adaptor

Unfortunately, testing reveals that the Palm Pilot adaptor will not work with most GPS units unless it is physically modified as it is not wired properly for GPS use. You need to remove Pin-8 of the MiniDin connector on the Palm Pilot adaptor. You can do this with a long needle-nose pliers. Doing this may render the adaptor useless for its original purpose of working with the PalmPilot.

Please note that other off-the-shelf MiniDin8-to-DB9 connectors (other than those for the PalmPC or Digital Cameras) usually will not work as they are wired differently; and those that do will most probably need Pin 8 removed (as above). Since you need to physically destroy the cable to see if it will work, an off-the-shelf cable may not be the best solution and the few dollars you save will be wasted in trying to get the cable to work.

Please note that we cannot provide technical support for customers who are using their own cable combinations (such as the surgery above) as the opportunity for time-wasting testing, disaster and inexplicable failure is too great. Although you may suspect ulterior motives (our primary one is to reduce our support burden and to make things as easy as possible for the customer), we strongly recommend that you use our Generic PC Adaptor instead. Our products are backed by a money-back-guarantee and full support.

Can I power my GPS unit off my laptop?

The quick answer for the layperson: No

The detailed answer for the technogeek is that most handheld GPS units easily exceed the maximum current draw limitations on devices for your PowerBook and desktop Macintoshes. Furthermore, most GPS units require 12VDC input, which is not provided by the Macintosh on external ports.

If you want to power your GPS unit externally, we recommend that you purchase the manufacturer's power/data cable, which usually come with a 12VDC "cigarette lighter" power-plug and a PC-style DB9 data cable attachment. You can then use our "Generic PC to Macintosh data cable adapter" to connect it to your Macintosh. Your GPS will then run off your car/motorcycle/boat's power supply.

In more detail, the issues with trying to use the PowerBook as a power source are:


Can I power my GPS off my USB?
This is an interesting idea. The USB port provides about 500ma @ 5VDC, however if you have an unpowered hub (such as the Apple keyboard) you will get considerably less. Since a simple hack won't provide the bus with knowledge of how much power you are drawing, you risk damaging the USB circuitry; although we would guess that the USB design is better protected against circuit fault than the ADB port since it supports hot-swapping. Just don't blame us if you cause hardware damage (as usual). Note that most GPS units need more than 5VDC on their external power inputs to operate.

Can I power my GPS off my FireWire port?
This is another interesting idea, but we're not sure of the power and voltage draw capabilities of the FireWire port. If you know, please e-mail us at .


Powering the GPS from the ADB port
It is rumored that the ADB port on the Macintosh supplies +5VDC for ADB devices on Pin 3 grounded to Pin 4 (Signal GND). Unfortunately, it is also said that ADB is rated for 100ma per device and is usually protected by a non-replaceable motherboard fuse. Some PowerBook models have even lower power specifications such as allowing only one low-power device to be connected via ADB. Please cross-check with the Apple specs on your machine. However, if we were to recommend using the ADB port for GPS power and a user either shorted or exceeded the power requirements and burnt our her/his motherboard fuse, we could be held liable. Thus, we cannot provide any information on this topic nor do we recommend that users use ADB power since we cannot accept any liability for damages caused by erraneous information or misapplication of information. Please note that a PowerBook motherboard replacement is in the range of $500-$2000+ and may not be covered under your warrantee if it is determined that a non-Apple product caused the damage.

Can I power my GPS off my GeoPort?
It is rumored that according to the PowerBook 3400 design notes, the 9th pin in the GeoPort MiniDin-9 configuration usually provides +5VDC at 300 mA grounded to Pin 4 (Signal GND) and is normally protected by a non-replaceable motherboard fuse. Other PowerMac and Performas are said to have a 100 mA maximum current draw limitation. Please cross-check with current Apple specs on your machine. However, if we were to recommend using the GeoPort for GPS power and a user either shorted or exceeded the power requirements and burnt our her/his motherboard fuse, we could be held liable. Thus, we cannot provide any information on this topic nor do we recommend that users use GeoPort power since we cannot accept any liability for damages caused by erraneous information or misapplication of information. Please note that a PowerBook motherboard replacement is in the range of $500-$2000+ and may not be covered under your warrantee if it is determined that a non-Apple product caused the damage.

How do I hook up a GPS receiver to my USB port?

Macintosh computers use USB ports rather than the standard serial ports found on PCs. This presents problems as many GPS units expect standard serial ports for communication.

The simplest and cheapest solution is the Keyspan USB Serial Adaptor which costs about $40. This adaptor ends in a PC-style DB-9 connector which you can hook right up to any standard GPS unit's PC data cable. We've verified that it works with GPSy X and GPSy ProX. [Keyspan PDA Adaptor]
[Keyspan USB PDA Adaptor]

In depth: Note that it is impossible to simply wire an adaptor cable between a USB serial bus and a standard serial device (such as a GPS unit). The USB Serial Bus standard is an intelligent bus, which means that you have to have an intelligent bus controller chip notify the bus master (computer) what configuration your device is, how much power it's using, etc. This bus intelligence is why USB is plug and play; but it means you can't use your older serial devices without a special adaptor box with its own integrated intelligence.

You will need to purchase a "USB to Serial" port adaptor. This device connects to your USB bus and allows you to attach standard Macintosh serial devices (including PDAs, modems, serial printers, etc.) to your USB-only Mac. The adaptors, from Keyspan and other companies, are relatively low-priced, all of the shipping units go for $40-$70.

If you have more information, please contact us.

The Keyspan USB Serial Adaptor seems to "jam" occassionally when downloading data from my Garmin

It appears the Keyspan USB Serial Adaptor that we've been selling has some bugs. Notably, it doesn't like the baud rate changing. This happens a lot when you're downloading or uploading data using the Garmin protocol. The constant switch between NMEA-0183 (4800bps) and Garmin Protocol (9600) confuses the Keyspan adaptor. There are three and a half solutions:

  1. Make sure you have the latest Adaptor driver software from Keyspan
  2. Quit GPSy and unplug the Keyspan adaptor, plug it back in and restart GPSy. This seems to reset the adaptor's circuits.
  3. When uploading or downloading, set GPSy's real-time protocol to NMEA-0183 @ 9600bps8N1 this prevents the unit from changing speeds and getting confused.
  4. Complain to Keyspan that their USB driver is buggy.

We're investigating better workarounds.

Can I mount my GPS on my motorcycle?

Written by Karen Nakamura

Yes! Handheld GPS units are ideal for motorcycle navigating. I've used three generations of GPS units on my Honda CX 500. The first was a Garmin GPS 12XL which I simply kept in my fuel-tank map bag's clear top compartment. The only problem was that when I was riding, my body blocked the GPS satellite signals. This was fine since I couldn't read the display safely while riding anyway, so it was most useful when I stopped at a traffic light or rest stop in order to confirm my location and heading. But you have to turn the GPS off to conserve batteries (since it's not getting a reading anyway while riding) which means that you have to wait while it initializes and finds itself when you turn it back on.

Next came a Garmin GPS II mounted onto my handlebar with a Garmin handlebar mount. The Garmin handlebar mount is a bit fragile and I broke the first one. Luckily, NavTech GPS (the store I purchased it from was more than happy to replace it, but mentioned that Garmin went through a round of bad plastics for a while. I deeply question the use of plastic on a mount that will go through the type of vibration on a motorcycle we're talking about.

After that came a GPS III and then a Garmin GPS III+ using the same handlebar mount. The built in highway maps were a dream and I used VirtualPC to upload my local street maps. I program all of my waypoints in using topo maps and street maps using GPSy. I can read the display while riding since the unit is mounted right by my right brake lever. Very handy. I've logged over a thousand miles using this setup. I've pulled power from my electrical system to power the unit. Luckily, my fuse box is located right under the ignition key on the handlebar so it was easy to pull a line. I'll post a photo here soon.

Most recently, I have a Garmin eMap that I mount using a CycoActive eMap mount. The mount is very solid, much better than the stock Garmin mount and is vibration isolated. It leaves the side power/light button and bottom data/power connector open for easy access, but otherwise cocoons the unit securely. I can't see the eMap popping or breaking out of this mount unless there was a major collision. I like the eMap's removable data cartridges because I can program a whole cross-country trip into them, down to the street level. The total price for the CycoActive mount including shipping was $42. Highly Recommended.

Note: Garmin sells handlebar mounts for most of their GPS units, but as I've mentioned, they're plastic and a bit flimsy. I recently was made aware of some third-party mount vendors. These look considerably more industrial, but I haven't had the chance to test them out yet. Caveat emptor (buyer beware):

Note that most of these should also mount fine on a bicycle, snowmobile, or jet ski (personal watercraft). Also, Global Mapping Systems has been sponsoring some interesting initiatives, including a man who is bicycling from Alaska to Florida as well as a women's motorcycle tourney across the U.S. See more info in our press room.

How do I mount my GPS on my boat or car?

On a large, stable boat, mounting your computer in the (dry) cockpit isn't usually a problem. You may have issues if there's a possibility of water getting in. The best thing may be to mount the GPS or GPS antenna in the wet space; then use a long serial extension to pull the NMEA signals into a dry cabin where you keep your computer. Or, you could investigate means of weather proofing your iMac or iBook -- we would advise looking into data "kiosk" type enclosures.

We don't recommend mounting your computer in your car for real-time use since it would be a tremendous road hazard to be looking at your computer while driving. If you promise to only use the computer while parked on the side of the road, we can recommend the use of "executive organizers" that mount in the passenger seat and provide a stable desktop environment (complete with penholders). Check your local automotive superstore for these things, they are basically a largish tabletop that mounts via the seat belt system.

One vendor for a variety of mounting systems for boats and cars is: Ram Mounting Systems

Can I unplug my GPS while my computer is on?

We've had several questions from clients who use GPSy on machines with only one available serial port that they share between several devices (GPS, modem, printer, etc.). They wonder if it's safe to plug and unplug the GPS from the serial port while the computer is still on, or if they should shut it down. Most GPS receiver data ports are designed to take abuse, so there's relatively little danger on the GPS end. The question is about the Mac.

For PowerBooks: the safest thing is to simply put the machine to sleep. It's safe to plug and unplug serial devices on all PowerBook models while they're asleep.

For other machines: the main issue is accidentally shorting out the serial port when plugging in a new device. The MiniDin8 pins are quite fragile, as many of you know from hard experience. It's easy to accidentally break or bend a pin inserting a device and short out the port; while some of the serial ports have built-in circuit breakers, on others, you burn out a chip on the motherboard that requires the whole board to be swapped. Expensive unless you're on a service plan.

If you really need to "hot swap" serial devices, consider investing in an inexpensive serial AB switch. This will let you switch between 2-4 serial devices just by rotating a dial or pushing a switch; and it's safe to unplug any device that's not switched to the Mac. You can buy these at any large computer store for $10-20. There are also programmable switchers that automatically switch to the right device for $50-$100.

The other advantage of switch boxes is that they relieve stress and strain from your poor Mac's serial port. The serial connector can only take so much before it breaks, and again this is an expensive motherboard swap item. Moving the action over to an inexpensive serial switch box makes things much safer at home on all fronts.

Alternately, you can buy a serial "extension cord" that comes with a female MiniDin8 on one end and a male on the other. This will not only make it easier to plug and unplug devices, but also relieve the stress on the motherboard connector of your Mac. It does't however alleviate the risk of short-circuiting the motherboard accidentally.

What is a Framing Error or Buffer Overrun Error?

When using GPSy or GPSy Pro, you may notice some error warnings appearing the GPS Data Monitor window. These usually look something like: Framing Error or Buffer Overrun.

Framing Errors are normally encountered when you first turn on your GPS unit or hook it up to your computer. In order to communicate properly, your GPS unit and Macintosh serial port hardware must synchronize. This usually takes one or two bytes before the byte frames align. After the frames align, communication should work smoothly without errors from that point onward. Therefore, one or two framing errors at the beginning of data reception are normal.

If all you get are framing errors without any data coming through, then this is a good indication that you are most probably at the wrong serial bps (baud) rate or parity. Go to the Serial preferences and change the bps rate/parity. Make sure you are using the right protocol. We recommend NMEA-0183 @ 4800 bps and 8N1 parity for normal real-time data communications.

If you get framing errors when you jiggle the data cable, then this is a good indication of a bad hardware connection. Make sure the cable is plugged in all the way. If you bought the cable from us, contact for assistance.

Buffer Overruns occur when the incoming data from the GPS unit overflows the incoming data buffer in GPSy. The program normally can buffer several seconds worth of data, but if you have a slow computer compounded by many data windows open, other applications running, or have the GPS unit set to a high bps rate, it is possible to overrun the data buffer. This should not normally occur with most Macintosh computers.

If you get buffer overruns, first see if you can set your GPS unit to output data at the normal NMEA-0183 rate of 4800 bps. Then, quit any other applications that might be running and close any GPSy windows that you aren't using. As buffer overruns should not normally occur, please contact for assistance if necessary.


Copyright (C) 1997-2007 by Global Mapping Systems and Karen Nakamura. All rights reserved. GPSy® and GPSy.COM® are registered trademarks and GPSy ProTM and GPSyLinkTM are trademarks of Karen Nakamura. All other trademarks are the property of their respective owners. Mention of a third-party's product does not represent endorsement of or by that product.

This page was last updated on Feb 19, 2007. We've had [N/A] hits since March 2nd, 1998.