Registers:
We know that a Flip-Flop can store a 1 bit of digital information (1 or 0) .It is also referred as 1-bit register. Registers find application in a verity of information in digital systems including microprocessor. For example Intel’s 8085 microprocessor contains seven 8-bit registers and five 1-bit registers.
The data can be entered in serial (1-bit at a time) or in parallel form (all the bits simultaneously) and can be retrieved in serial or parallel form. Data in serial form is called temporal code where as data in parallel form is called special code. A 4-bit data 1010 is shown in fig a) and in parallel form in fig b).
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registers using flip flops
Registers are classified depending upon the way in which the data are entered and retrieved. There are four possible modes of operations:
- Serial-in ,serial-out (SISO)
- Serial-in, parallel-out (SIPO)
- Parallel-in, series-out (PISO)
- Parallel-in, parallel-out (PIPO)
Registers can be designed using various Flip-Flops (S-R or J-K as D-type) and are also available as MSI devices.
Registers in which data are entered or/and taken out in serial form are referred as shift registers, since bits are shifted in the Flip-Flops with the occurrence of clock pulses either in the right direction or in the left direction or in both the directions (Bi-directional). IC74295A is a bi-directional shift register.
A register is referred as universal register if it be operated in all the four possible modes and also as bi-directional registers. For example 74194 is a universal register.
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