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AR# 21445

Schematic - "ERROR:DesignEntry:20 - Pin '' is connected to a bus of a different width"


When I run a process on my schematic design module, the following error occurs:

"Started process "View HDL Functional Model".

ERROR:DesignEntry:20 - Pin "<pin_name>" is connected to a bus of a different width."


Before a schematic design is implemented, it is first converted to either Verilog or VHDL (depending on the setting of the Generated Simulation Language property). As part of the conversion process, a Design Rule Check (DRC) will be run on the selected schematic and any underlying schematics. "Error: DesignEntry:20" indicates that the bit width of a symbol pin does not match the bit width of the net connected to the pin.

Example: The D input of an FD component is connected to a net named data(3:0). The pin bit width is 1 and the connected net bit width is 4.

In the ISE Schematic Editor, the pin bit width must match the bit width of the net connected to it.

To pull a specific bit (or bits) off a bus to connect it to a symbol pin of a lesser width, use name association. In the example above, the third MSB bit of data(3:0) can be used to drive the D input of the FD by connecting a net to the D input and naming it "data(2)."

If the symbol pin's bit width is greater than the width of the net that you will be connecting to it, a possible solution is:

For nets connected to input pins: Use a concatenated bus to add fill bits.

Example: A net named data(11:0) connects to the B(15:0) input of an ACC16 component. A net named "low" (connected to a GND component) could be used to pad the input data by connecting a floating net to the B(15:0) input and naming the net "low,low,low,low,data(11:0)."

For nets connected to output pins: Connect a bus net with width matching the pin width to the pin, but use just the portion of the bus that is needed.

Example: A user would like to use the two most significant bits of the Q(15:0) output of a binary counter. They connect a hanging net to the Q(15:0) output and name it cnt(15:0). The two most significant bits are then used by naming another net "cnt(15:14)."

AR# 21445
Date Created 09/04/2007
Last Updated 12/15/2012
Status Active
Type General Article