- (Review) Flip Flops
- There are multiple types of flipflops
- Our discussion is limited to D flip-flops
- Two inputs, D - the signal to (possibly) store
- CK, a control signal, indicates store value of D
- Output Q, the stored value
- When CK changes from 0 to 1, the value of D is stored
- This is an edge triggered device, it only changes the value when
the control signal changes from 0 to 1
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- an level-triggered device changes state any time that the
control signal is a 1
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- Registers
- A register is a collection of flip-flops with a common control line
- The above example has a two-bit register
- Common operations on registers include, load, store, shift left
- There is a picture of a load/shift register on page 58, please look
at it.
- Feedback Loops - The output of a storage unit is used to determine its
next state.
- Control Timing Signals
- A signal used to control a circut
- Repeats a signal changing from 0 to 1
- The period is the length of time for a pattern to repeat
- The pulse is where the signal is 1
- The leading edge is the transition from 0 to 1
- The trailing edge is the transition from 1 to 0
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- Control signals are tied to the timing signal.
- The leading edge of a control signal starts with the trailing edge
of a timing signal.
- A control signal may last for more than one timing signal period.
- Encoders/Decoders
- A decoder accepts n inputs and produces 2n outputs.
- Input: A binary number
- Output: The corresponding line 1, all others 0.
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i0 |
i1 |
o0 |
o1 |
o2 |
o3 |
0 | 0 | 1 | 0 | 0 | 0 |
0 | 1 | 0 | 1 | 0 | 0 |
1 | 0 | 0 | 0 | 1 | 0 |
1 | 1 | 0 | 0 | 0 | 1 |