Hi @TeemoLi
I hope that you are doing well!
According to the LPC845 Datasheet, the minimum voltage for VDD is 1.8v.
The normal operating voltage is 3.3v.
As a general reply, if the voltage is below the specification there is no guaratee for the MCU to behave properly.
The LPC845 integrates an brownout protection mechanism, which maintains the device in a reset if the VDD voltage falls below the expected. Because if the VDD specifications are not meet, the device may malfunction.
This a general reply from my side. If you have more concerns about this or more details, like the test situation or scenario that you are facing to get 1.3v, do not hesitate to let me know.
All the best,
Diego
