Does anybody happen to know what kind of serial cable is required to connect the RS-232C (25-pin) serial port on a Philips PM3350 oscilloscope to a PC? Specifically, I'm wondering if the PM3350 uses the additional lines present on 25-pin serial ports but not on 9-pin ones and whether it's a DTE or DCE device.
It's a male RS-232C port on the 'scope, does that mean it's a DTE?
You could try the following tests to determine the nature of the scope serial port. Use an oscilloscope probe and look at each pin in the DB-25 connector. Output pins are going to show a +/- voltage in the ranges over a couple of volts positive or negative. Inputs will typically make a small jump in the scope trace. Don't expect more than noise level signal for inputs but it gives you a clue of connected circuitry. It should also be possible to use a 10-12K resistor pulled off first to +V and then to -V to pull the "input pins" away from their floating near ground state. No connect pins in the connecor typically display a smooth flatline on the scope. Finally the GND pin can be verified via the resistor not being able to pull that pin above or below the zero volt level.
Before you start a test like this you can greatly simplify the test process and increase the reliabilirty of the results if you can guess as what the pins the connector are normally connected to. For example for a DB25 it is quite normal to expect the TxD and RxD signals on the pin 2 & 3 pair. One should show output and the other input. This could also point toward your answer for the DCE/DTE question.