Duplex not working on HP CLJ 4700 and others

Hi,

I am pretty new to PS programming and I read quite some FAQ and articles on PS programming and enabling duplex printing on the device.

My wishes are pretty straight forward: All pages shall be printed duplex, no tumble.

So I added right after the prolog comment the following code:

%%EndProlog

%%BeginSetup
    <<
        /Duplex true
        /Tumble true
    >>
        setpagedevice
%%EndSetup

%%Page: formtemplate_v14_1 1

Unfortunately the printer could not care less.

I have now a huge pile of simplex printed pages on my desk and no clue what I am missing.

If you can help, go ahead. I am printing using the prfile32 utility using a HP 4700 CLJ printer. It is attached on the network HPdirect port and I have installed the universal printer driver from HP.

I will provide you the PS file, but cannot attch it here, since the function is disabled.

Any help appreciated - even RTFM, if you provide me a vector...

Thanks in advance!

Thomas