http://www.sbb.ch/en/station-services/am-bahnhof/dhl-service-point/automatic-ticket-machine.html Explains the ticket machines. So cash would be fine. Visa Debit card isn't listed, Visa credit card is. Isn't your Visa also maestro-enabled?
Because Visa debit cards are processed through the same system as Visa credit cards, provided your Visa debit card is not in some way blocked from international use it will also work fine.
I *have* however noticed problems with a few UK cards, noticeably some issued by the Co-operative Bank/Smile, when using them in Switzerland at SIX Card Services terminals, which is what SBB use. If this problem occurs the machine will appear to freeze for a few minutes but then declines and returns your card. So the first time you use any UK card in a Swiss ticket machine ensure you do it in plenty of time for your train in case this occurs and you have to wait for the decline then go and obtain cash (which is also generally accepted, though it won't take big notes for small fares at the TVM).
By the way, if you do want a full year's Halbtax and will visit Switzerland twice a few weeks apart, unless it's changed with the Swiss Pass you can have it issued to be sent to the station of your choice for collection. You also get a one-month provisional version on a ticket blank for initial use.
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Just in case the OP isn't already aware, Swiss rail tickets are expensive, even allowing for use of the half fare card. You can however buy a one day SBB pass for CHF 73 (valid all day though there is a cheaper version available for travel after 09:00). This can only be purchased with a valid half fare card. There is more information on the SBB website but I'm on a mobile & can't post the link at present.
You'd be surprised - you have to do a lot of travel before that becomes worth it.
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AFAIK The former does not convert into an 'all line' day rover as does the latter.
I don't know if this is the case or not, but it would surprise me, as SBB has always had a simple fares structure, so it would seem odd for it to work with one type of Halbtax and not the other. You may of course be right though - your signature certainly shows this as being your area of expertise
Best way to be sure is to purchase the first one from a staffed station, as SBB tend not to take prisoners with the hefty (CHF 90) Penalty Fares.
FWIW from my reading the "Swiss Pass" seems to be a smartcard (ITSO style) that can contain any number of different travel products, one of which is the Halbtax.
