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Altera_Forum
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13 years ago

My First CPU but.. one problem

Hello to all, I completed my first CPU in VHDL, an incredibly satisfying feeling! : D I simulated successfully but I did not understand what it means to a signal colored red in ModelSim: ht...
Altera_Forum's avatar
Altera_Forum
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13 years ago

High impedance should only be used on external pins when it is required (usually on a bidirectional bus).

On internal signals the FPGA hardware isn't capable of putting a line in high impedance, so if you use it the synthesizer will change it to OR gates. It is absolutely possible to use it inside an FPGA design but it is considered bad practise because it doesn't correspond to the generated hardware.