
Flash*Freeze Mode
IGLOO PLUS Starter Kit User’s Guide
33
IGLOO PLUS I/O State in Flash*Freeze Mode
In IGLOO PLUS devices, users have multiple options in how to configure I/Os during Flash*Freeze
mode:
1.
Hold the previous state.
2.
Set I/O pad to weak pull-up or pull-down.
3.
Tristate I/O pads.
The I/O configuration must be configured by the user in the I/O Attribute Editor or in a PDC constraint file, and can
be done on a pin-by-pin basis. The output hold feature will hold the output in the last registered state, using the I/O pad
weak pull-up or pull-down resistor when the FF pin is asserted. When inputs are configured with the hold feature
enabled, the FPGA core side of the input will hold the last valid state of the input pad before the device entered
Flash*Freeze mode. The input pad can be driven to any value, configured as tristate, or configured with the weak pull-up
or pull-down I/O pad feature during Flash*Freeze mode, without affecting the hold state. If the weak pull-up or
pull-down feature is used without the output hold feature, the input and output pads will maintain the configured weak
pull-up or pull-down status during Flash*Freeze mode and normal operation. If a fixed weak pull-up or pull-down is
defined on an output buffer or as bidirectional in output mode, and a hold state is also defined for the same pin, the pin
will be configured in hold state mode during Flash*Freeze mode. During normal operation, the pin will be configured
with the predefined weak pull-up or pull-down. Any I/Os that do not use the hold state or I/O pad weak pull-up or
pull-down features will be tristated during Flash*Freeze mode and the FPGA core will be driven high by inputs. Inputs
that are tristated during Flash*Freeze mode may be left floating without any reliability concern or impact to power
consumption.
Table 4-2
shows the I/O pad state based on the configuration and buffer type.
Table 4-1 · Flash*Freeze Mode Type 1 and Type 2 – Signal Assertion and Deassertion Values
Signal
Assertion Value
Deassertion Value
Flash*Freeze (FF) pin
Low
High
LSICC signal
High
Low
Notes:
1. The Flash*Freeze (FF) pin is an active-Low signal, and LSICC is an active-High signal.
2. The LSICC signal is used only in Flash*Freeze mode type 2.
Table 4-2 · IGLOO PLUS Flash*Freeze Mode (type 1 and type 2)—I/O Pad State
Buffer Type
Hold State
I/O Pad
Weak Pull-Up/-Down
I/O Pad State in
Flash*Freeze Mode
Input
Enabled
Enabled
Weak pull-up/pull-down
1
Disabled
Enabled
Weak pull-up/pull-down
2
Enabled
Disabled
Tristate
1
Disabled
Disabled
Tristate
2
Notes:
1. Internal core logic driven by this input buffer will be set to the value this I/O had when entering Flash*Freeze mode.
2. Internal core logic driven by this input buffer will be tied High as long as the device is in Flash*Freeze mode.
3. For bidirectional buffers: Internal core logic driven by the input portion of the bidirectional buffer will be set to the hold state.
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