IGLOO Low-Power Flash FPGAs with Flash*Freeze Technology
2- 54
Advanced v0.1
I/O State in Flash*Freeze Mode
When the device enters Flash*Freeze mode, I/Os will
become tristated. If the weak pull-up or pull-down
feature is used, the I/Os will maintain the configured
weak pull-up or pull-down status. This feature enables
the design to set the I/O state to a certain level that is
determined by the pull-up/-down configuration. For
example, use the output buffer and enable weak pull-
down to drive a signal LOW to an external component
while the IGLOO device is in Flash*Freeze mode.
configuration and buffer type.
Note that configuring weak pull-up or pull-down for the
FF pin is not allowed.
Flash*Freeze Mode Design Considerations
Entering Flash*Freeze Mode
The device was designed and optimized to enter
Flash*Freeze mode only when power supplies are
stable. If the device is being powered up while the FF
pin is asserted (Flash*Freeze mode type 1) or both FF
pin and LSICC signal are asserted (Flash*Freeze mode
type 2), the device is expected to enter Flash*Freeze
mode within 5 s after the I/Os and FPGA core have
reached their activation levels.
If the device is already powered up and then the
FF
pin
is
asserted,
the
device
will
enter
Flash*Freeze mode within 1 s (type 1). In
Flash*Freeze mode type 2 operation, entering
Flash*Freeze mode is done within 1 s after both
FF pin and LSICC signal are asserted. Exiting
Flash*Freeze mode is done within 1 s after
deasserting the FF pin only.
If an embedded PLL is used, entering Flash*Freeze
mode will automatically power down the PLL.
The PLL output clocks will stop toggling within
1 s after the assertion of the FF pin in type 1, or
after both FF pin and LSICC signal are asserted in
type 2. At the same time, I/Os will transition into
the state specified in
Table 2-30. The user design
must ensure it is safe to enter Flash*Freeze mode.
During Flash*Freeze Mode
Inputs and input clocks to the FPGA can toggle
without any impact on static power consumption,
assuming weak pull-up or pull-down is not
selected.
If weak pull-up or pull-down is selected and the
input is driven to the opposite direction, power
dissipation will occur.
Any
toggling
signals
will
be
charging
and
discharging the package pin capacitance.
Outputs will be tristated, and the output of the
input or bidirectional buffer tied to the internal
logic will be set to logic 1. Refer to
Table 2-30 for
more information.
JTAG operations such as JTAG commands, JTAG
bypass, programming and authentication cannot
be executed. The device must exit Flash*Freeze
mode before JTAG commands can be sent.
The FF pin must be externally driven (deasserted)
for the device to stay in Flash*Freeze mode.
The FF pin is still active; i.e., the pin is used to exit
Flash*Freeze mode when deasserted.
Table 2-30 Flash*Freeze Mode (type 1 and type 2)—I/O Pad State
Buffer Type
Internal Weak Pull-Up/-Down
I/O Pad State in Flash*Freeze Mode
Input
Enabled
Weak pull-up/pull-down*
Disabled
Tristate*
Output
Enabled
Weak pull-up/pull-down
Disabled
Tristate
Tristate output buffer
E = 0 (tristate)
N/A
Tristate
E = 1 (output)
N/A
Tristate
Bidirectional
E = 0 (input)
Enabled
Weak pull-up/pull-down*
Disabled
Tristate*
E = 1 (output)
Enabled
Weak pull-up/pull-down
Disabled
Tristate
Note: *Internal core logic driven by this input buffer will be tied to logic 1 as long as the device is in Flash*Freeze mode.