I'm learning about pipelining but can't understand this abbreviation: "CL". You can see it in processors' schemes.

It is shown with with and without a line above it; what is the line for?

enter image description here

Diagram taken from here http://lgjohn.ecen.ceat.okstate.edu/4243/lectures/unpiped.pdf - page 3.

  • 2
    \$\begingroup\$ "clock", maybe? \$\endgroup\$
    – jippie
    Sep 28, 2013 at 10:13
  • 1
    \$\begingroup\$ If not clock, as jippie suggests, you should add a diagram were you found this abbreviation. \$\endgroup\$ Sep 28, 2013 at 10:33
  • \$\begingroup\$ Where did you find this diagram? \$\endgroup\$
    – Renan
    Sep 30, 2013 at 22:18
  • 1
    \$\begingroup\$ The line above is binary inversion. \$\endgroup\$
    – Ben Voigt
    Sep 30, 2013 at 23:14

2 Answers 2


In the PDF file the text under the diagram is "With the clock wired as shown, the A and B data bus are driven from data read from the register file when CL is high, and the busses are driven from the ALU when CL is low".

Although not explicitly stated, I think the author intended CL to mean "CLock".

When the CLock is high the register file values are presented to the ALU input latches, and when the CLock subsequently becomes low the output from the ALU is presented to the buss and written to the register file by asserting W (Write)...which I suspect should have been marked on the diagram as bar-W.

  • \$\begingroup\$ Great man, i want myself killed for my negligence \$\endgroup\$
    – Yola
    Oct 1, 2013 at 14:24

I was going through some of the lecture slides and I have come to the conclusion that: CLK: Clock CL: Capacitor used with Crystal Oscillator

  • \$\begingroup\$ The accepted answer says CL = clock, and by the diagram CL is clearly not a capacitor, so the information on your slides is not applicable here. \$\endgroup\$
    – Wesley Lee
    Nov 18, 2016 at 21:46

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