See Also

FUNCTION TRI (in, oe)
   RETURNS (out);

COMPONENT TRI
   PORT (a_in : IN STD_LOGIC;
      oe: IN STD_LOGIC;
      a_out: OUT STD_LOGIC);
END COMPONENT;

The TRI primitive is a tri-state buffer with an input, output, and output enable signal. If the output enable input to the TRI buffer is high, the output will be driven by the Input.

The output enable defaults to VCC.

If the output enable of a TRI buffer is connected to VCC or a logic function that will minimize to true, a TRI buffer may be converted into a SOFT buffer during logic synthesis. In ACEX^® 1K, APEX^™ 20KC, APEX 20KC, APEX^™ II, ARM^®-based Excalibur^™, Cyclone^™, FLEX 10KE, Mercury^™, Stratix^™, and Stratix^™ GX projects, some configurations of TRI primitives and other logic are automatically converted into OPNDRN buffers.

When you use a TRI buffer, you must observe the following rules in addition to the rules listed in Primitive/Port Interconnections:

• A TRI buffer may drive only one BIDIR pin. You must use a BIDIR pin if feedback is included after the TRI buffer.

• If a TRI buffer feeds logic, it must also feed a BIDIR pin unless it is part of a tri-state bus. If it feeds a BIDIR pin it may not feed any other outputs.

Inputs IN OE		Output OUT
X	0	Z
1	1	1
0	1	0

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