Answers Database
FPGA Compiler: Pullup/Pulldown Resistors are Deleted From Synopsys Design
Record #1757
Problem Title:
FPGA Compiler: Pullup/Pulldown Resistors are Deleted From Synopsys Design
Problem Description:
Urgency: Standard
General Description:
Instantiated pullup/pulldown resistors may be deleted from your
design during the compile process in FPGA Compiler versions V3.4b
and earlier. This is a known Synopsys problem that will not be fixed in
a future release of Synopsys FPGA Compiler I.
This issue does not apply to FPGA Express or FPGA Compiler II.
Solution 1:
To solve this problem, do not instantiate pullup/pulldown resistors for I/O
applications. Instead, use the set_pad_type -pullup|-pulldown port_name
command to achieve the same result.
For internal applications (such as wired-AND or mux functions built using
wide edge-decoders or tristate buffers), use the following commands to
re-insert the pullup/pulldown once it has been removed by the compile
process. When targeting XC4000E/EX devices, execute the replace_fpga
command as usual and then use the following commands:
create_cell an_instance_name_of_your_own_creation
xgen_4000[e|ex]/PULLUP
connect_net find(net, target_net_name) find(pin,
your_instance_name/O)
Examples:
replace_fpga
create_cell pullup1 xgen_4000e/PULLUP
connect_net find(net, SIGNAL_C) find(pin, pullup1/O)
create_cell pullup2 xgen_4000ex/PULLUP
connect_net find(net, SIGNAL_B) find(pin, pullup2/O)
create_cell pulldown1 xgen_4000ex/PULLDOWN
connect_net find(net, SIGNAL_A) find(pin, pulldown1/O)
End of Record #1757 - Last Modified: 04/13/99 09:37 |
