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Zynq-7000 AP SoC Technical Reference Manual www.xilinx.com 163
UG585 (v1.11) September 27, 2016
Chapter 6: Boot and Configuration
External Reset Signal Pins
There are two external reset pins:
PS_POR_B: This reset is used to hold the PS in reset until all PS power supplies are at the
required voltage levels. It must be held Low during PS power supply ramp-up. PS_POR_B can be
generated by the power supply “power-good” signal. The POR reset is the only reset to sample
the boot mode pin strap resistors.
Note: PS_POR_B must not be de-asserted during a certain timing window relative to when the
last PL power supply starts to ramp. Asserting PS_POR_B during this window can cause a
lock-down event. Refer to section 6.3.3 BootROM Performance: PS_POR_B De-assertion
Guidelines, page 177 for more details.
PS_SRST_B: This reset is used to force a system reset. It can be tied or pulled High, and can be
High during the PS power supply ramp-up. The PS_SRST_B reset is a non-POR reset.
Note: The PS_SRST_B signal must not be asserted while the BootROM is executing from a POR
reset, otherwise a lock-down event occurs and prevents the BootROM from completing the
system boot process. To recover from this type of lockdown, the PS_POR_B reset must be
asserted. The time taken by Boot ROM to complete its execution and handoff to the FSBL/user
application depends on the several factors. Please refer to Boot Time Reference, page 220 for
details on how to arrive at the boot time for a specific user configuration.
Reset Signal Sequencing
The reset sequencing required for boot are illustrated in Figure 6-4. The effects of the resets are
described in this chapter and in Chapter 26, Reset System. If PS_SRST_B is asserted while the
BootROM is executing, then a system lockdown occurs without an error code being generated.
X-Ref Target - Figure 6-4
Figure 6-4: Power and Reset Sequencing Waveform
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