Answers Database

Proseries: Design Manager: CPLD Fitter trims pins (IOPADs) when designing Bidir bus


Record #1421

Product Family:  Software

Product Line:  EPLD Core

Problem Title:
Proseries: Design Manager: CPLD Fitter trims pins (IOPADs) when
designing Bidir bus



Problem Description:
The fitter will trim IO pins that have the inputs left hanging.

			   IO_0
(logic) 0ut_0 >-----|>----o-------<IOPAD>
		   obuf   |
			  |-----------|>------* IN_0(left unconnected)
				     ibuf

This is most common when using designing a BiDirectional bus.  Although all of
the outputs of the IOPAD are used, some of the inputs driven by an IPAD4,8,16
may not be used.


Solution 1:



Workaround:  If the bus components are used, convert the design
to use the single OBUFs, IBUFs, and IOPADs.  Then, remember not
to connect IBUFs to the IOPADs where the inputs won't be used.
Just connect an OBUF to the IOPAD.  An IBUF can always be added
if needed for future designs.  This will prevent the software
from finding a hanging input, and the IOPAD will be left
intact.

			 IO_0
(logic) 0ut_0 >-----|>------------<IOPAD>
		   obuf

M1FX



End of Record #1421