Sitecom USB-to-Serial adapter


Hi all,

Encouraged by several recent posts about using USB-to-Serial adapters, to connect an HP-48 to modern PCs without serial ports, I went and bought such an adapter myself: a Sitecom (model number CN-104).

Just like the other users reported (for different models from different brands), it works well. Under Linux (Fedora Core 3), it is recognized automatically and shows up as /dev/ttyUSB0; I can upload and download to my HP-48G using C-Kermit, and I can download pictures from my Olympus D-340R (using gphoto2) as well.

On the Windows side (XP sp2), I had to install a driver (from the included CD-ROM), and then the adapter shows up as COM4. It is possible to make it show up as any COM port; COM4 is just the default (possibly because COM3 is my laptop's built-in modem). I could then use Olympus' Camedia Master software to talk to my camera.

I haven't tried talking to the HP-48G from Windows XP yet. Does anyone have suggestions as to what software to use? Is it possible to compile C-Kermit under Cygwin, or should I pony up the $48 for Kermit 95, or are there other good alternatives?


- Thomas



you can use MS-DOS KERMIT,

which also works in a DOS box in XP.

An alternative wuld be GSZ,

which features X,Y,Z-Modem .




Windows XP comes with Hyperterminal. That's what I use to do my file transfers when I boot Windows XP. There is an HP48/49 connectivity package from which first loads the HP48 with an xmodem server. From there, all file transfers are drag-and-drop via the PC.


The 16 bit Windows app Transfile48 works well, too. It opens two windows, one of which is local and the other is remote. Transfile48 uses Kermit as its underlying protocol and doesn't install any special software on the 48.



Any Kermit-based application that works with your operating system
and can use the ("virtual"?) COM port should work with any 48 or
49 series, except the 49g+. They all have both Kermit and Kermit
Server built-in, although a rather basic version of them.

With the 49g+, you'd also have to convert to IrDA or USB. I've
used the 49g+ with HyperTerminal and an RS-232/IrDA converter
(with Win98SE supplying a virtual COM port), but haven't been able
to get Conn4x to work with IrDA. Conn4x works with the 49g+'s USB,
and I believe that applications for Apple and Linux operating
systems are also available.

The 49 series (including the 48gII) has the Xmodem Server
built-in. As far as I know, this Xmodem Server is unique to these
HP calculators.

The 48G/GX/G+ has Xmodem built-in, but doesn't have Xmodem Server
built-in, although an Xmodem Server library is available. For any
application that expects an Xmodem Server, install the library.

The 48S/SX doesn't have Xmodem built-in, so to use an Xmodem-based
application with it, you'd have to find (or develop) an Xmodem
application, and in some cases, an Xmodem Server. Xmodem for the
48S/SX might be availabe at

All 48 and 49 series also have "Serial I/O" commands built-in, so
you could always develop your own communications protocol,
although for file transfers, that seems to me much like
re-inventing the wheel. But note that the XON/XOFF software flow
control capability was intentionally removed from the 49 series,
so you'd have to be careful not to overrun the 255-byte input
buffer. You might want to provide for error checking.

Working in assembly language, you can ignore the RPL input buffer
and build a string in temporary memory, and then replace its bytes
one at a time, as long as your routine is fast enough to check the
UART again by the time the next byte arrives. Again, you might
want to provide for error checking.

Besides HyperTerminal, HPComm, the Kermit-based "Connectivity Kit"
for the 49G, works with any 48 or 49 series. See

To use Conn4x, the Xmodem-based "Connectivity Kit" for the 49g+,
on a 48G/GX/G+, you'll have to install the Xmodem Server Library
(included with Conn4x) on the calculator. This library doesn't
work with the 48S/SX, although I suppose that one that does could
be developed. Be sure to use only the most recent version (Version
2.2 Build 2353, as far as I know) of Conn4x, available at

HP's site



I tried the Kermit-based connectivity kit, but I couldn't get it to work. There was clearly some attempt at communication going on (messages flashing in the calculator's display etc.), but despite quadruple-checking all communication parameters, I kept getting Could Not Connect To The Calculator type messages.

I then tried the latest Conn4x package from HP's web site. I was a bit worried about having to install a library on the 48G, but the process turned out to be painless (the documentation is good and the application even gives step-by-step instructions). The library takes up about 3500 bytes on the calculator but that's not a problem, since I only use the calculator occasionally and don't keep huge data sets or programs on it.

Conn4x works fine, so I'll stick with that (and continue to use C-Kermit under Linux).

Thanks to all for your advice!

- Thomas


The problem with running kermit programs under Windows XP is that they are usually DOS-based applications. Since Windows XP rarely provides hardware permissions to the command prompt (supposedly like a DOS environment), you will unlikely be able to use these kermit programs. (Under the older version of Windows like 95 or 98, they should work just fine).


I was referring to hpcomm, which is similar to Conn4x in that it provides an explorer-type user interface with drag and drop, but it uses the kermit protocol to talk to the calculator (unlike Conn4x, which uses xmodem).

According to the documentation, hpcomm should work on WinNT and Win2000 (as well as 95 and 98), but I couldn't get it to work on my laptop, which runs XP. I don't know if XP is the problem, or the fact that I was using a USB-to-Serial converter rather than a "standard" COM port (which my laptop doesn't have). I thought hpcomm looked rather buggy anyway; it appears that it hasn't been updated in years.

- Thomas

Edited: 20 May 2006, 9:26 a.m.

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