Your initial post says that your mod-12 counter is supposed to count from 15 to 4. The "mod-12" merely indicates that it has 12 states that it cycles through. The "15 to 4" tells you what those 12 states are, namelyI know what T-ff is and i i kinda understand what mod-12 counter does, but not completely. Like i understood that means that i need to reset counter when it gets to 12, so it can start from begining. I hope you understand what i'm trying to say.
Before you start doing truth tables, you need a state diagram and, from that, a state transition table.Oh, that was confusing to me, i think i understand it little better now.
So, counter has to start at 15, then count down to 4. When it gets to 4 then needs to be reset. Am i right?
Can i draw a truth table and send it so you can tell me is it right?
I think that this is explained in every Digital electronics book. There are some steps which you need to follow and that's it. It is explained very well in Digital Fundamentals by Thomas Floyd for example. Roughly speaking, you draw state diagram first, then you write transition table for T flip flop (every flip flop has its own transition table) and after that you have enough informations to fill k-maps, which are necessary to find logical connections between flip flops which make counter. Design procedure is always same, regardless of flip flop type used. So once when you are familiar with design using T flip flops for example, you can design using other types of flip flops also.I need to make mod-12 asynchronous down counter using T flip flop. It counts from 15 to 4. I don't know really how to do it and it's really important, so if you could help me i would be very grateful!
The state transition table doesn't really indicate whether it is synchronous or asynchronous. You could draw up a table for a ripple binary counter and it would look the same as the table for a synchronous binary counter. Where the different come in is what comes next -- the excitation logic. For a synchronous design you craft the logic for the control inputs of the FF, for an asynchronous design you craft the logic for the clock (and/or asynch set/reset inputs). Therein is where the demons lay in wait.
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