Actual binary decimal 0001 1 2 0101 3 p a g e

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Actual Binary Decimal 0001 1 ? 2 ? 0101 ? ? ? ?
3 | P a g e Discussion Registers are useful for storing and manipulating digital information. An electronic register is a kind of memory that uses a series of flip-flops to store the individual bits of a binary code, such as a byte (8 bits) of data. The size of the stored binary code depends on the number of flip-flops that make up the register. In short, register simply means a group of flip-flops . In addition, the number of flip-flops is equal to the number of bits a register can store. D Flip-flops Flip-flop is a 1-bit memory cell which can be used for storing the digital data. It uses combinations of NAND gates as shown in the figure. D flip-flop has two inputs: signal D and CK (clock). Q and Q(not) are its output. CK is usually connected to a 555 timer IC which is a pulse generator. Input D could be set as “low=0” or “high=1”. In D flip-flop, changes in D input will not affect the output Qs if the clock is low=0 (see truth table below). Figure below shows the timing diagram of clock CK, D input and Q output. The Clock pulses at constant interval from A to K . D input was selected as: low at A to B , changes to high at B to H , low at H to J and high at J to K . In the Q output , you may notice that input D registers only when the clock is high which causes a delay between D and Q.
4 | P a g e Timing diagram of D flip-flop Parallel In - Parallel Out (PIPO) Registers You already know that the bit size of a register is equal to the number of flip- flops used in a circuit. If we desire to increase the capacity of a register to 4 bits, what we need is to use four (4) flip-flops. Figure in the next page shows a simple 4-bit register consisting of four D flip-flops, sharing a common clock input, providing synchronous operation ensuring all bits are stored at exactly the same time. The binary code (“0” or “1”) to be stored is applied to the four D inputs (D 0 , D 1 , D 2 & D 3 ) and is registered by the flip-flops at the rising point of the next clock (CK) pulse. The stored data are now ready from the Q outputs (Q 0 , Q 1 , Q 2 & Q 3 ). It remains if the circuit has power, or until new data on the D inputs is saved with a rising edge of another clock pulse. This process also overwrites the previous data. Shown in the figure at the left side is a simplified symbol of a PIPO register with 4 parallel inputs (D 0 , D 1 , D 2 & D 3 ) and 4 parallel outputs (Q 0 , Q 1 , Q 2 & Q 3 ). You only need to add below the D 3 and Q 3 if additional inputs and outputs are required.
5 | P a g e Shift Register Shift registers are devices capable of shifting stored bits laterally in one direction or vice versa. These have a similar structure to the PIPO register but have the added ability to shift the stored binary word one bit at a time (of clock pulse) from left to right or in opposite directions. Shift register consists of a chain of flip-flops in cascade.

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