HP48 gx Connectivity Tips

After battling with the hp48 for a couple days over connection problems, I wanted to share some of my findings with the community.

I am using the hp48 as data collector (with TDS surveying software) for my surveying business. I borrowed it from a friend, and didn't get the full story with how to download data from it to my PC. My current setup is using a Windows XP PC that has a COM port.

Wanting to connect to the hp48, I searched the web and found several programs that connect to the calculator: the original Kermit DOS program, hp48explorer, HPcomm Connectivity Kit, and Conn4x. After I connected the hp48, set up the transfer settings, and put it into server mode, nothing would work for me.

So here are a few pointers for those of you that have the same headaches as I have had:

1. Serial cable

I highly recommend finding the original serial cable that came with the calculator to hook it up to a PC. But if that is not an option, I have found a good set of instructions on how to build your own serial cable here (about 3 quarters down that page):
I managed to find a serial mouse that was mentioned in the article at Radio Shack and I snagged a tiny connector that fits into the hp48 jack from an old CDROM. The connector that the author of the link is talking about isn't found in newer computers.

Note: for surveyors who use an "environmental case" with a serial connection, see surveyors' topic below.

2. Device Manager settings

Even after a good serial cable is hooked up to the computer's COM port, you still might have problems connecting to a PC. All the programs I mentioned above would still not recognize the calculator I was using. I found that the COM port might need to be freed up.

If your computer has a dial-up modem installed, you need to disable it (hopefully you are using a separate LAN card for your internet connection). The modem that is installed (mine is an old 56k) will usually be taking up the COM1 port. My setup had a modem that was taking up COM3 and a "communications cable" that was taking up COM1.

Go to the Properties menu of My Computer.
Go to the Hardware tab.
Click Device Manager.
Under Modems, right click on any modems that are installed and choose Disable.
Under Modems, right click any "connection cable between two computers" and choose Disable.
Close all windows.

This should free up the COM port and allow you to connect to the PC.
I was able to connect no problem after this.

3. Surveyor's environmental case

If you use an environmental case with your hp48, you may have problems connecting that case to your PC.

I am using the hp48 with an environmental case to connect to a TOPCON GPT3000 total station and using the TDS software for surveying commands. That environmental case (a plastic case to protect from the elements) has a serial port that connects to the hp48 serial jack. The serial port works great with the TOPCON instrument, but wouldn't allow me to connect to the computer.

I found out that the RX (receiving) pin and the TC (transmitting) pin on the case port was switched when it was soldered on. This naturally had something to do with the way the TOPCON instrument communicates with the hp48.

The proper pin arrangement is this:
(see this website: http://www.faqs.org/faqs/hp/hp48-faq/part3/ )

HP48 rs232-9 serial cable
1 shield, not needed
2 2
3 3
4 5

Where HP48 pin 1 is the pin closest to the upper right side of the calculator screen.

I found this out the hard way when I tried to connect the case to the computer with a female-female rs232 serial cable. I got errors like "unexpected packet received" and "could not open port".

If the female-female serial cable is the route you want to take, you need to cut the cable in half, find out which wires go to which pins (you only need pin 2, 3, and 5), and then switch the 2 and 3 pin wires. Keep the pin 5 wire where it is. And try to figure out which end belongs to which device.

Note: I had a radio shack RS-232C cable, part number 26-152B.
Here is the procedure I took:
Cut the wire so there is a short piece (hp48) and a long piece (computer).
Keep the yellow wire together (pin 5).
On the short side (hp48) connect the red wire to the brown wire on the long side (PC).
On the short side (hp48) connect the brown wire to the red wire on the long side (PC).
Connect the short side to the hp48 environmental case and the long side to the computer.

I do not recommend this option, try to connect directly to the hp48 and cut out the middleman.
(see above for where find out how to make your own serial cable.)

4. Surveyor's software.

To get your data our of the calculator (the coordinate file and the RAW file), you need to use a surveying software program. The above mentioned programs (Kermit, hp48explorer ... etc) cannot retrieve these files.
I recommend Carlson Survey or TDS Foresight. Both are available as free trials offers if you need them in a pinch.

The instructions for downloading from Carlson is found here:

That's all. Good luck.


I think you should copy that into the ARTICLES forum, which doesn't go way into Archive land. It is a very nice reference summary!

You might get some good feedback here that you can add to it, too.


Someone here, I think (obviously I forget who) suggested I get a serial to USB converter and then plug my HP-48G and HP-48G+ into a USB port on my WinXP PC when I had connectivity issues.

That worked, but only if I use a particular one of the connectivity programs you mentioned with it. Again, I forget which one, though I just used it several weeks ago; I think it was Conn4x. I'll check and repost on this thread. The others couldn't see the calculator.

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