Reset Controller
UG0331 User Guide Revision 15.0
644
Figure 277 •
Power on Reset Delay Configuration
The delay counter is used to generate the power supply rise time. All power supplies must be stable
within the configured Power on Reset Delay. When the counter reaches its maximum value, the
PO_RESET_N signal is de-asserted. Upon de-assertion of the PO_RESET_N signal, the 1 MHz RC
oscillator is gated off and the 50 MHz RC oscillator is enabled and the System Controller starts operating
at 50 MHz clock. Then System Controller starts the initialization sequence of I/O banks, MSS, and FPGA
Fabric Subsystem.
The POWER_ON_RESET_N signal is generated from the PO_RESET_N signal and can be used in the
user design as a reset for the FPGA fabric logic. It is an active low output signal. It is made available by
instantiating the SYSRESET macro from the Libero SoC IP catalog in SmartDesign or by instantiating the
SYSRESET macro directly in the HDL file. The following figure shows a block symbol of the SYSRESET
macro that exposes the POWER_ON_RESET_N signal.
Figure 278 •
SYSRESET Macro
POWER_ON_RESET_N asserts on the following events:
•
Power-up event
•
Assertion of DEVRST_N
•
Completion of programming
•
Completion of zeroization
A dedicated input-only reset pad (DEVRST_N) is present on all the SmartFusion2 devices, which cause
assertion to the PO_RESET_N signal. If an external reset circuit is connected to the DEVRST_N pin, it
increases the power up to functional time due to the delays that the external reset device does add.
DEVRST_N is an asynchronous reset pin and must be asserted only when the device is unresponsive
due to some unforeseen circumstances. It is not recommended to assert the DEVRST_N pin during
programming operation, which might cause severe consequences including corrupting the device