User guide

68 www.xilinx.com Spartan-6 FPGA Configuration User Guide
UG380 (v2.7) October 29, 2014
Chapter 4: User Primitives
rollover is desired, the DOUT port can be connected directly to the DIN port to allow for
the same data to be shifted out after completing the 57-bit shift operation. If no additional
data is necessary, the DIN port can be tied to a logic zero. The attribute SIM_DNA_VALUE
can optionally be set to allow for simulation of a possible DNA data sequence. By default,
the Device DNA data bits are all zeros in the simulation model.
SUSPEND_SYNC
The SUSPEND primitive extends the capabilities of the user to synchronize the design for
applications using the suspend mode. It uses a three-pin interface to allow synchronization
of the trigger to start the suspend mode, even when there are several clock domains
requiring synchronization. The three signals are: SREQ, SACK, and CLK.
SREQ outputs a request to the fabric to begin a suspend mode. SACK acknowledges that
the fabric is ready to start the suspend mode. The SACK pin is synchronous to the CLK pin.
Table 4-4:
DNA_PORT Port Descriptions
Signal Name Direction Function
DOUT Output Serial-shifted output data.
DIN Input User data input to the shift register.
READ Input Synchronous load of the shift register
with the Device DNA data. A READ
operation overrides a SHIFT
operation.
SHIFT Input Active-High shift enable input.
CLK Input Input clock to the shift register.
Table 4-5: DNA_PORT Attribute
Attribute Type Allowed Values Default Description
SIM_DNA_VALUE 57-bit vector 57'b0, any 57-bit
value
All zeros Specifies a DNA value for
simulation purposes (the actual
value is specific to the particular
device used).
Table 4-6: SUSPEND Port Description
Signal Name Direction Function
CLK Input User clock.
SACK Input SUSPEND Acknowledgement; synchronous to CLK.
SREQ Output Suspend request from SUSPEND pin.