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:
Platform(s): Workstations
Architecture(s): All
Design Step(s): Compile (FPGA Compiler only)
Reference Number: Not Available
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 is scheduled to be fixed in a future relea
se of Synopsys.


Solution 1:

To solve this problem, do not instantiate pullup/pulldown resistors for I/O appl
ications. Instead, use the set_pad_type -pullup|-pulldown port_name command to a
chieve the same result.
For internal applications (such as wired-AND or mux functions built using wide e
dge-decoders or tristate buffers), use the following commands to re-insert the p
ullup/pulldown once it has been removed by the compile process. When targeting X
C4000E/EX
devices, execute the replace_fpga command as usual and then use the following co
mmands:

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