How can I solve this error?

ERROR:Pack:1107 - Unable to combine the following symbols into a
single IOB
   component:
   	BUF symbol "TXD_OBUF" (Output Signal = TXD)
   	PAD symbol "TXD" (Pad Signal = TXD)
   Each of the following constraints specifies an illegal physical
site for a
   component of type IOB:
   	Symbol "TXD" (LOC=R7)
   Please correct the constraints accordingly.

E.Can ODACIOGLU

On Jul 28, 7:47=A0am, Eyyub Can Odacioglu
<ecodacio...@gmail.com> wrote:
> How can I solve this error?
>
> ERROR:Pack:1107 - Unable to combine the following symbols into a
> single IOB
> =A0 =A0component:
> =A0 =A0 =A0 =A0 BUF symbol "TXD_OBUF" (Output Signal =3D TXD)
> =A0 =A0 =A0 =A0 PAD symbol "TXD" (Pad Signal =3D TXD)
> =A0 =A0Each of the following constraints specifies an illegal physical
> site for a
> =A0 =A0component of type IOB:
> =A0 =A0 =A0 =A0 Symbol "TXD" (LOC=3DR7)
> =A0 =A0Please correct the constraints accordingly.
>
> E.Can ODACIOGLU

Get out the datasheet for your part.  What type of pin is location
R7?  If it is
not an I/O pin (i.e. input only or special purpose pin) you can't use
it as an
output pin.

Regards,
Gabor