The MMIO class allows a Python object to access addresses in the system memory mapped. In particular, registers and address space of peripherals in the PL can be accessed.

AXI GP ports

In an overlay, peripherals connected to the AXI General Purpose ports will have their registers or address space mapped into the system memory map. With PYNQ, the register, or address space of an IP can be accessed from Python using the MMIO class.


MMIO provides a simple but powerful way to access and control peripherals. For simple peripherals with a small number of memory accesses, or where performance is not critical, MMIO is usually sufficient for most developers. If performance is critical, or large amounts of data need to be transferred between PS and PL, using the Zynq HP interfaces with DMA IP and the PYNQ DMA class may be more appropriate.


In this example, data is written to an IP and read back from the same address.

IP_BASE_ADDRESS = 0x40000000

from pynq import MMIO

data = 0xdeadbeef
mmio.write(ADDRESS_OFFSET, data)
result =

This example assumes the memory mapped area defined for the MMIO, from 0x40000000 to 0x40001000, is accessible to the PS.

More information about the MMIO module can be found in the pynq.mmio Module sections