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I need to clear up a problem with an external input to a CPLD by putting it through a tristate buffer. I know Quartus II has a tristate-buffer megafunction, but I am curious – if I simply tell it to output Z on the specific pin, will in automatically synthesize so the tristate buffer is enabled on that pin, or do I have to implement the function/write a buffer?
You can do it either way. If you assign ‘Z’ to the pin (NOTE: it has to be an upper-case Z, lower-case confuses Quartus) a tri-state buffer will be inferred. Alternately, you can directly instantiate various low-level I/O primitives which have a tri-state enable pin (including various DDR I/O primitives).
I have generally allowed Quartus to infer the tri-state buffers on ‘normal’ I/O pins, and used the low-level primitives when timing is critical and I want to force use of the I/O ring flip-flops, use the DDR I/O features, etc.