I bought a serial cable from hpcalc to use the serial port on the HP50g.

At first we couldn't get it working, then we found that the OPENIO command
was needed and I guess it operates a little differently than on the HP 48.

In the process of troubleshooting, we hooked the HP 50 to my son's
Oscilliscope to observe the output, if any.

On the calculator we ran a simple program:

<< DO "M" XMIT DROP .01 WAIT UNTIL 0 END >>

This repeatedly sent the bits for a capital M character.
We used the M because is has both two adjacent high bits and alternate
high-low combinations. We also tried a capital U, which nicely has
alternating high and low bits.

Then, we did the same for a 48g and 48gx to see how they compare.

The signal for the 50g does have a higher amplitude (higher voltage)
and while the 48g and gx exhibited some timing jitter, the cable from
HPcalc on the 50g had much more stable timing.

Everything worked fine! We took pictures of the o-scope, but I don't know
how to share them here in a newsgroup.

Now that we have proved that the cable is working good, we will go back to
hooking the 50g to a Zebra 105sl Label Printer.