# Change PS frequency on PYNQ-Z1

**URL:** <https://discuss.pynq.io/t/change-ps-frequency-on-pynq-z1/8774>\
**Category:** Support\
**Created:** [September 23, 2025, 2:05pm UTC](https://discuss.pynq.io/t/change-ps-frequency-on-pynq-z1/8774 "2025-09-23T14:05:15Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![Koyiott](https://sea1.discourse-cdn.com/flex019/user_avatar/discuss.pynq.io/koyiott/32/7270_2.png) [@Koyiott](https://discuss.pynq.io/u/Koyiott)\
**Post date:** [September 23, 2025, 2:05pm UTC](https://discuss.pynq.io/t/change-ps-frequency-on-pynq-z1/8774/1 "2025-09-23T14:05:15Z")

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Hi all,

I am working on a PYNQ-Z1 board and I would like to change the processing system (PS) frequency, specifically the APU clock, from the default (~667 MHz) down to around 85 MHz.  
From the PYNQ Python API I know we can adjust the PL clocks (FCLK0..3), this works for the PL, but it does not affect the PS CPU clock.

The APU frequency is fixed by the FSBL/BOOT.BIN at boot time? Can I change it with the generated bitstream on Vivado?

Could someone confirm the correct procedure for running the CPU at a different clock (e.g. 85 MHz)?

Thanks in advance!