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In a design, a gated clock (which is combinatorial logic used as a clock signal) should follow the following guidelines:
The gating logic should be a two-input AND
gate or a two-input OR
gate.
There should be only one input pin that acts as a primary input clock signal to the AND
or OR
gate.
The non-clock input clock enable signal to the AND
or OR
gate should be synchronized with a register. The register should be clocked by the same input pin that acts as the primary input clock signal to the AND
or OR
gate.
If the gated clock uses an AND
gate, the clock port of the register that drives the AND
gate should be active on the falling edge and the clock port of the register driven by the AND
gate should be active on the rising edge.
or
If the gated clock uses an OR
gate, the clock port of the register that drives the OR
gate should be active on the rising edge and the clock port of the register driven by the OR
gate should be active on the falling edge.
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