ralliesport said;
Oh and it will be illegal to drive a truck with a digital tacho if you dont have a card
Absolutely correct, do not even think of taking a digital equipped vehicle if you do not have a drivers smart card. That said, there are a limited number of circumstances where you can drive without a drivers card;
a) You live in a Member State that has not started issuing smart cards. That doesn’t apply to anybody ‘living’ in UK as DVLA started issuing cards in June of this year.
b) your card has been lost / stolen or is malfunctioning. Under these conditions you must report the matter to the competent authority (in the UK that is DVLA) within 7 days. If the card is lost / stolen abroad you should also report this to the Police in the area where the loss / theft happened, this should prove most amusing for those of us who have ever tried informing the Police abroad of anything other than our bank account number
. DVLA then have 5 working days to get your replacement card to the local DVLA office or VOSA Test Station of your choice, so you can collect the replacement. You can drive for upto 15 days, or longer if necessary to reach base, without a smart card.
BUT; in either a) or b) above you MUST at the end of each day make an activity print from the Vehicle Unit (VU). You have to sign the printout, put your FULL name on it and also your driving licence number or your smart card number. You then treat the printout as you would any tachograph chart (so simmer in red wine for 20 minutes and eat with lashings of brown sauce
) Alternatively produce like you would a chart currently; all records for this week and the last one from the proceeding week in which you drove.
ralliesport also wrote;
If you do and also drive analogue you have to take a print off from the digital tacho, but dont ask me why.
No printout required as the record will be on your drivers smart card unless a) or b) above apply.
coffeeholic wrote;
For the same reason we have to carry a certain number of charts now. If you are stopped while driving an non digital tacho truck but have driven a digital one earlier in the week, or 28 day period as it will then be, you have to be able to show a complete record and the print out will do that.
Agreed Neil, if the regulations change so you must show 28 days worth of records you will have to carry any analogue charts used during that period. You will also have to produce your digital smart card if you have one. But you only need produce printouts if either a) or b) above apply within the period. Otherwise it is the records held on your smart card that count. Whilst the card can hold upto 28 days worth of data, you have to remember that if you use the card on days 1,3,4,5 and drive analogue equipped vehicles on day 2 and 6 your card will only have 4 records on it. The record on day 29 overwrites the record for day 1, day 30 overwrites day 2 etc.
coffeeholic also wrote;
Depends if the person stopping you has a computer and the software to read the card or not I guess, having the print out means that they will still be able to check regardless.
Doen’t matter what equipment the inspecting person has (or hasn’t) your record is the driver card and not the printouts (unless a or b apply). Any inspecting officer can obtain printouts using the VU of either you smart card contents or the VU contents or both. Both driver and operator are obliged to make sure sufficient printer paper is available for this purpose. The paper is type approved by the way (like charts) and you must make sure you have the right one for the VU. I know this one is going to upset enforcement officers abroad, but if they don’t have the kit to interrogate your smart card, that is not your problem, you are not required to carry printouts to make them feel better.
ralliesport said;
Also say you work with the same wagon with a digital card but you are asked to drive on with a analogue system, will you be braking the law because you havent taken print outs of your preious 27 days?
Not unless a) or b) above apply, you simply smile and produce your driver card.
FINALLY, an enforcement officer cannot take a drivers smart card and retain it unless one of the following apply:
c) the card was obtained using false documents or by deception
d) a driver is using a card that doesn’t belong to them, should be pretty easy to check, the officer just looks at the photograph 
e) the card is forged or has been tampered with, again pretty easy to spot, a hole is drilled thru the chip or a photo is stuck over the original on the card.
Sorry this was a long post but digital tacho has lots of ‘issues’ with it, what do you expect when the legislation runs to over 230 pages!