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manual: explain $tribuf cell.

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whitequark 2019-01-14 16:08:58 +00:00
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manual/CHAPTER_CellLib.tex
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@ -119,6 +119,12 @@ than one bit from \B{S} is set the output is undefined. Cells of this type are u
``parallel cases'' (defined by using the {\tt parallel\_case} attribute or detected by ``parallel cases'' (defined by using the {\tt parallel\_case} attribute or detected by
an optimization). an optimization).
The {\tt \$tribuf} cell is used to implement tristate logic. Cells of this type have a \B{WIDTH}
parameter and inputs \B{A} and \B{EN} and an output \B{Y}. The \B{A} input and \B{Y} output are
\B{WIDTH} bits wide, and the \B{EN} input is one bit wide. When \B{EN} is 0, the output \B{Y}
is not driven. When \B{EN} is 1, the value from \B{A} input is sent to the \B{Y} output. Therefore,
the {\tt \$tribuf} cell implements the function \lstinline[language=Verilog]; Y = EN ? A : 'bz;.
Behavioural code with cascaded {\tt if-then-else}- and {\tt case}-statements Behavioural code with cascaded {\tt if-then-else}- and {\tt case}-statements
usually results in trees of multiplexer cells. Many passes (from various usually results in trees of multiplexer cells. Many passes (from various
optimizations to FSM extraction) heavily depend on these multiplexer trees to optimizations to FSM extraction) heavily depend on these multiplexer trees to
@ -476,6 +482,10 @@ Add information about {\tt \$dffe}, {\tt \$dffsr}, {\tt \$dlatch}, and {\tt \$dl
Add information about {\tt \$\_DFFE\_??\_}, {\tt \$\_DFFSR\_???\_}, {\tt \$\_DLATCH\_?\_}, and {\tt \$\_DLATCHSR\_???\_} cells. Add information about {\tt \$\_DFFE\_??\_}, {\tt \$\_DFFSR\_???\_}, {\tt \$\_DLATCH\_?\_}, and {\tt \$\_DLATCHSR\_???\_} cells.
\end{fixme} \end{fixme}
\begin{fixme}
Add information about {\tt \$\_TBUF\_} cells.
\end{fixme}
\begin{fixme} \begin{fixme}
Add information about {\tt \$\_NAND\_}, {\tt \$\_NOR\_}, {\tt \$\_XNOR\_}, {\tt \$\_ANDNOT\_}, {\tt \$\_ORNOT\_}, Add information about {\tt \$\_NAND\_}, {\tt \$\_NOR\_}, {\tt \$\_XNOR\_}, {\tt \$\_ANDNOT\_}, {\tt \$\_ORNOT\_},
{\tt \$\_AOI3\_}, {\tt \$\_OAI3\_}, {\tt \$\_AOI4\_}, and {\tt \$\_OAI4\_} cells. {\tt \$\_AOI3\_}, {\tt \$\_OAI3\_}, {\tt \$\_AOI4\_}, and {\tt \$\_OAI4\_} cells.