Some points to note from the ASX guidance note (
http://www.asx.com.au/documents/rules/gn16_trading_halts.pdf)
1) Maximum of 2 consecutive trading halts of maximum 2 days are allowed (i.e. maximum 4 days trading halt). Any longer and it needs to be a voluntary suspension
2) Participants can't place orders, amend orders or trade in the security (only can cancel orders).
3) Purging of all existing orders occurs at the end of the day the suspension was ordered or if being re-instated on the same day purging occurs before the security is placed into the 'pre-notice received session state' as a precursor to the resumption of trading
4) ASX usually ends voluntary suspension once the entity makes the announcement about the event it said would result in the lifting of the suspension, without the need for the entity to take further action on its part
5) If for any reason an entity is not in a position to make the announcement about the event it said would result in the lifting of the suspension within the time that it originally anticipated, the entity is expected to make an announcement to inform the market of the reasons for the delay, and the new date by which it expects the suspension to be able to be lifted.
Hope this clears up some questions people have been having!