Recap: Registers A register is a single byte (or word) memory element. Once written to (clocked) it remembers the input byte and outputs the same number regardless of further changes at the D input… …until the next clock input of course. CLK D 0-7 Q 0-7 D 0-7 Q 0-7 CLK 8 8
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Recap: Registers A register is a single byte (or word) memory element. Once written to (clocked) it remembers the input byte and outputs the same number.
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Recap: Registers
A register is a single byte (or word) memory element.
Once written to (clocked) it remembers the input byte and outputs the same number regardless of further changes at the D input…
…until the next clock input of course.
CLK
D0-7 Q0-7D0-7 Q0-7
CLK
8 8
Interconnecting Registers
Interconnecting registers in a computer is like building roads to connect towns on a map:
Silly wayn towns require (n2-n)/2 roads
A
C
B
E
D
Interconnecting Registers
Interconnecting registers in a computer is like building roads to connect towns on a map:
Sensible wayFar fewer
roads, (but lesser
capacity)
A B
C
E
D
Interconnecting Registers
CLK
D0-7 Q0-7
CLK1
8 8
CLK
D0-7 Q0-7
CLK2
8 8
CLK
D0-7 Q0-7
CLK3
8 8
8
Register Connections
Data can be written from any register to any other register
Limitations Only one data transfer can happen at once In general, this is how computers work. They can only do a small number of very
simple operations… …and they can only do one of them at a time. But, they do it very quickly!
Bi-directional Connection
Connections from the common bus to the registers are bi-directional.
CLK
D0-7 Q0-7
8 8
CLK
Input / Output
8
Set of 8 digitally controlled switches
Input / OutputControl
Tri-State Ports
This arrangement is often known as a tri-state port.
Each input/output line can have three possible states: When being read from (input/output is low)