[SOLVED]Can not connect pi with pl2303

[jhello]

Um..I have already posted on http://www.raspberrypi.org/phpBB3/viewtopic.php?f=91&t=62682
But I think it is the OS that matters because the one who connected pi with pl2303 successfully uses rasbian but I use arch.
I think maybe arch doesn't use GPIO as the port controls pi by default?
I paste the problem here...
Anyone could help?
Thanks very much!
----------
I try to connect pi with pl2303,but all I get is nothing.
My laptop OS is Kubuntu 1204 with ckermit installed.
$this->bbcode_second_pass_code('', 'sudo kermit
SET LINE /dev/ttyUSB0
SET CARRIER-WATCH OFF
c')
then
$this->bbcode_second_pass_code('', 'Connecting to /dev/ttyUSB0, speed 115200
Escape character: Ctrl-\ (ASCII 28, FS): enabled
Type the escape character followed by C to get back,
or followed by ? to see other options.
----------------------------------------------------')
with nothing followed.
Then I exit kermit and create ~/.kermrc
$this->bbcode_second_pass_code('', 'set line /dev/ttyUSB0
set speed 115200
set carrier-watch off
set handshake none
set flow-control none
robust
set file type bin
set file name lit
set rec pack 1000
set send pack 1000')
But it doesnt help.
Could anyone tell me what the problem is or what I should do?
Thanks very much!
+++++ADDED+++++
My pi's OS is archlinux,maybe it matters?

[WarheadsSE]

Check that you have the Tx paired to Rx and vice versa. And don't connect Vcc!

[jhello]

To WarheadsSE:
Oh!Thanks!
I changed tx/rx connection but with vcc connected,and it works!

[pepedog]

Don't connect vcc

[jhello]

To: pepedog
Um..Do you mean I should connect with 3 lines,TXD to RXD,RXD to TXD,GND to Ground?
But without the other line connected,kermit shows
$this->bbcode_second_pass_code('', 'Connecting to /dev/ttyUSB0, speed 115200
Escape character: Ctrl-\ (ASCII 28, FS): enabled
Type the escape character followed by C to get back,
or followed by ? to see other options.
---------------------------------------------------- ')
No login prompt...
The power light on pi doesn't shine,so I guess...if I don't use another usb power adapter I should connect vcc?
I am confused...

[pepedog]

You are powering the pi via this connection?

[jhello]

To:pepedog
Yes..should I?And which one should I connect 3.3v or 5v?

[WarheadsSE]

You should not be powering the Pi via the serial port.

[jhello]

To:WarheadsSE
OK.Thanks very much!