20
www.xilinx.com
Spartan-6 FPGA Power Management
UG394 (v1.1) September 4, 2012
Chapter 1:
Power Management With Suspend Mode
Do not use any other JTAG instructions when in suspend mode or while transitioning into
and out of suspend mode. Furthermore, do not enter suspend mode when performing a
readback operation.
SUSPEND Pin
When the suspend feature is enabled (see
Enable the Suspend Feature and Glitch Filtering,
page 14
), the SUSPEND pin controls when the FPGA enters suspend mode. During normal
FPGA operation, the SUSPEND pin must be Low. When High, the SUSPEND pin forces the
FPGA into the low-power suspend mode.
Table 1-5
describes the functionality of the
SUSPEND pin.
If the suspend feature is not enabled for an application (the application never enters
low-power mode), then connect the SUSPEND pin to GND. Do not leave the pin floating
or High.
Characteristics
The SUSPEND pin is an LVCMOS/LVTTL receiver, and power to the input buffer is
supplied by the V
CCAUX
power rail. The SUSPEND pin has no pull-up resistors during
configuration, and the HSWAPEN control has no effect on the SUSPEND pin.
Table 1-4:
JTAG Operations Allowed during Suspend Mode
Boundary-Scan
Command
Description
IDCODE
Read the JTAG ID code that describes the Spartan-6 FPGA array
type in the JTAG chain. This value is different from the Device
DNA identifier, which is unique to every device.
BYPASS
Enables BYPASS.
USERCODE
Read the user-defined code embedded in the FPGA bitstream.
Table 1-5:
SUSPEND Pin Functionality
ENABLE_SUSPEND
Settings
SUSPEND
Pin
Function
NO (default)
Suspend Mode
Disabled
0
The suspend feature is disabled. The SUSPEND pin is unused and ignored.
Connect the SUSPEND pin to GND.
Filtered, Unfiltered
Suspend Mode
Enabled
0
The FPGA performs the application described in the bitstream loaded into the
FPGA during configuration. When the SUSPEND pin changes from High to
Low, wake the FPGA from suspend mode. Return from suspend mode also
depends on the SCP pins, if used.
1
Force the FPGA to enter power-saving suspend mode pending SACK assertion
on SUSPEND_SYNC primitive, if used.
