Using PL2303HX to program 3.3v device

Using Arduino Programming Questions
#1

Hi

I would like to use a PL2303HX to program a 3.3v device.
The PL2303HX I've ordered has a 3.3v and 5v pin, but how do I tell what the RX/TX pins are running at?

5v will damage my device so I obviously want to make sure this does not happen and check my facts with someone else first.

Looking at the datasheet, the PL2303HX itself uses 3.3v so am I right in saying that it will be okay to use this module as it is, as opposed to the earlier versions that by default run at 5v?

Something that caught my eye though is the following statement:
"Supports RS-422/RS-485 like serial interface (TXD, DTR_N, and RTS_N pins should be externally pulled-up to 5V)"

Can I then just use a voltmeter directly on the pins to see what level they are pulled up to?
If they are pulled up to 5v, can I use a voltage divider to bring that down to 3.3v?
..Or I suppose I can try desolder the pull ups and use my own.

Any tips before I start causing damage?

Many thanks

Jason

#2

You can use a voltmeter to measure the voltage of the Serial pins (Serial pins are normally high, then are pulled low for data transmission).

If the UART operates at 3.3V, you can add a logic shifter on the Rx line of the 3.3V device (resistor between 3.3V Rx and 5V Tx, with a Zener between 3.3V Rx and GND).
The 5V device should be able to pick up the 3.3V Tx.

#3

SandraOos:
You can use a voltmeter to measure the voltage of the Serial pins (Serial pins are normally high, then are pulled low for data transmission).

If the UART operates at 3.3V, you can add a logic shifter on the Rx line of the 3.3V device (resistor between 3.3V Rx and 5V Tx, with a Zener between 3.3V Rx and GND).
The 5V device should be able to pick up the 3.3V Tx.

Thanks - I forgot about that option.

#4