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Visitor
djmds
Posts: 6
Registered: ‎11-29-2008
0

Spartan 3 inputs held low after configuration

Sorry, 1st post did not accept the attachment.

 

Circuit where input signals get held at a low level after Xilinx is configured.  As a test, I produced a simple design consisting of: input pad-> buffer -> output pad.  Input signals are present before configuration but are held low after configuration.  This happens whether the Xilinx is progammed via JTAG or via XCF01S configuration PROM.  I/O standards defined have been default, LVTTL, and LVCMOS33.  Vcco for the bank is 3.3V.  Input signal on GCLK7 (bank0) is not affected but input signals on all other bank 0 and bank 1 pins are affected including signal of GCLK6 (bank 0), GCLK5 (bank 1) and GCLK4 (bank 1).  PCB schematic attached.

 

Any and all help is appreciated.

Visitor
djmds
Posts: 6
Registered: ‎11-29-2008
0

Re: Spartan 3 inputs held low by Xilinx after configuration

Further info: All I/O's are being treated as unused.  If I set the unused pin option to "float" input signals are not affected.
Visitor
djmds
Posts: 6
Registered: ‎11-29-2008
0

Re: Spartan 3 inputs held low after configuration

Further info:  If I use an IBUFG the input are fine, if I use an IBUF the inputs are treated as unused I/O's.

 

Dave