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AR# 41288

13.1 Route - T enable signal in IOBUFDS connected to constants are not getting routed

Description

Unroutes reported in PAR when trying to connect the T enable to either GND or VCC.

WARNING:Route:436 - The router has detected an unroutable situation for one or more connections. The router will finish the rest of the design and leave them as unrouted. The cause of this behavior is either an issue with the placement or unroutable placement constraints.
To allow you to use FPGA editor to isolate the problems, the following is a list of (up to 10) such unroutable connections:
Unroutable signal: GLOBAL_LOGIC0 pin: iq_out_tx_n<0>/T
Unroutable signal: GLOBAL_LOGIC0 pin: iq_out_tx_n<1>/T
Unroutable signal: GLOBAL_LOGIC0 pin: iq_dci_n/T
Unroutable signal: GLOBAL_LOGIC0 pin: iq_out_tx_n<2>/T
Unroutable signal: GLOBAL_LOGIC0 pin: iq_dci_p/T
Unroutable signal: GLOBAL_LOGIC0 pin: iq_out_tx_n<3>/T
Unroutable signal: GLOBAL_LOGIC0 pin: iq_out_tx_p<0>/T
Unroutable signal: GLOBAL_LOGIC0 pin: iq_out_tx_p<1>/T
Unroutable signal: GLOBAL_LOGIC0 pin: iq_out_tx_p<2>/T
Unroutable signal: GLOBAL_LOGIC0 pin: iq_out_tx_p<3>/T

Solution

This is an unusual use case since the constant T enable creates the equivalent of an IBUF or OBUF functionality which should be used instead.

The problem with this design is that the T enable pin can only be driven by either the TOUT pin of the ODELAY (not used in this case) or the TQ pin of OLOGIC (used as OSERDES). This means that the T enable signal has to be run through the OSERDES component. This is true even for constants since there are no constant sources internal to the IOB.

This problem has been fixed on ISE 13.2 software.
AR# 41288
Date Created 03/20/2012
Last Updated 12/15/2012
Status Active
Type General Article
Tools
  • ISE Design Suite - 13.1
  • ISE Design Suite - 12.4
  • ISE Design Suite - 12.1
  • More
  • ISE Design Suite - 12.2
  • ISE Design Suite - 12.3
  • Less