Hi Winson,

I don't understand the need to display time in this project of yours. At most, you need a buzzer to indicate that the card is rejected (or forgotten in the reader once it's been validated!). If the users' access is limited to certains times, they should just check their watch!
Also, if the fact of reading a valid card opens a door (electric lock), remember that the first thing is to unlock the door, *then* log the event - waiting for a single-dot printer to print even 1 line is frustrating for the user (been there, done that!).

If you have several devices, perhaps use an RS422/485 communication line.
If you're opening a door & using a centralised validation scheme, the comms will influence the reaction time of the system (depending on Baud rate & number of devices). A way around this is to give some autonomy to the readers, but this means more complexity.

If you need to show the user some data from his card, then of course you will need an LCD, & the reaction time of the system becomes secondary, as the user will want to stop & read his info. All the reader has to do is read the data off the card, send it up to the PC when polled, & display the message sent back by the PC.

Regards,

Richard