ID:14818 Converted the fanout from the open-drain buffer "<name>" to the node "<name>" into a wire
CAUSE: The specified open-drain buffer feeds internal logic in addition to feeding tri-state logic. The Quartus Prime software converted the non-tri-state fanouts of this open-drain buffer to a wire because the chip does not support internal tri-states.
For example, the following Verilog design gives this warning message:
module test1 (input data, oe, output out, inout bidir);
wire triwire, gnd;
assign gnd = 1'b0;
assign triwire = oe ? gnd : 1'bz;
and(out, triwire, data);
assign bidir = triwire;
endmodule
In the design, the open-drain buffer triwire
feeds an AND
gate in addition to feeding the pin bidir
. As a result, the Quartus Prime software converts its fanout to the AND
gate to a wire, and gives this warning.
Note that an inversion is also an internal fanout. If an open-drain buffer feeds a pin through an inversion, the Quartus Prime software will convert the open-drain buffer into a wire. Additionally, if an open-drain buffer feeds another open-drain buffer, the Quartus Prime software will convert the first open-drain buffer to a wire. ACTION: Avoid this warning message by removing all the internal fanouts of the open-drain buffer.