AHDL: Parameterized Tri-State Bus (lpm_bustri)

This example implements a tri-state bus. The width of the bus is specified with the LPM_WIDTH parameter and can be changed for your design. The dq and data_out pins are fed by tri-state buses. Because tri-state buses cannot feed internal logic, you should use the lpm_bustri function only if dq and data_out feed pins. This example uses an Include Statement (shown in blue text) to import the contents of the Include File containing the Function Prototype of the lpm_bustri function. An Instance Declaration implements (shown in red text) an instance of the function.

For more information on using this example in your project, go to:

• How to Use AHDL Examples
• Graphic Editor: Parameterized Tri-State Bus
• Implementing Tri-State Buses in Altera Devices
• MAX+PLUS II Help

---

tribus.tdf

INCLUDE "lpm_bustri";

SUBDESIGN tribus
(
   enable_out, enable_in  : INPUT;
   datain[7..0]           : INPUT;
   dataout[7..0]          : OUTPUT;
   dq[7..0]               : BIDIR;
)

VARIABLE
  u1 : lpm_bustri 
        WITH (LPM_WIDTH=8);

BEGIN

   u1.data[7..0] = datain[7..0];
   u1.enabletr = enable_out;
   u1.enabledt = enable_in;
   dataout[7..0] = u1.result[7..0];
   dq[7..0] = u1.tridata[7..0];

END;

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