Is it ethical to request the advisor to share the registration fee for submitting a conference paper? My advisor and I have decided to present some resent research results in a well-known conference, selected based on our discussions. Now the aforementioned joint paper has been accepted and the clock's ticking to consider the payment of the registration. We have never talked about the financial aspect of this process. The cost associated with registration and transportation is quite high, but my advisor has not yet told me anything about any plan to take that into account and there are just a couple of days left until the payment deadline. I am wondering if he assumes that I myself must pay the fee, but I cannot afford the whole cost . If he expects me to pay all of that registration fee, I have to get over finalizing the registration and the conference, at all. In my perspective, the 50-50 code of ethics sounds fair enough. 

Is it ethical to talk about such a thing with the advisor?

If so, how would I supposed to explain and handle the case?
Talk to your advisor, now.  Dealing with funding and finances are a significant part of academic life; they aren't some shameful taboo thing.

Most academics don't pay for professional travel, including conferences, out of their own pockets; often funds are available from your institution, or from any grants that may be funding your project, or from the conference itself.  It's entirely reasonable to ask your advisor about funding sources that might be able to pay the cost for you attending this conference; you should also research possible funding sources yourself.

If funding isn't available, or can't cover the full cost, it's up to you to decide whether you want to spend your own money to go.  If you decide that you can't, that's okay; you just won't go.  I don't think people would see this as stinginess on your part, but rather a misfortune that no other funds were available.

However, by the same token, if your advisor tells you that he doesn't have any funds available to pay, you shouldn't expect him to dip into his own pocket.  

Ideas like your  "50/50 split" don't usually come up, unless there are multiple outside funding sources that could pay, and the question is how to apportion the costs between them.