Hi
i have one doubt..in apb protocols...what is the difference between wait_state and no_wait_state in apb protocopls?
Sections 3.1.1 and 3.3.1 of the APB protocol document describe transfers with no wait states (when PREADY is high while PENABLE is high), and 3.1.2 and 3.3.2 describe transfer with wait states (when PREADY goes low for all but the last cycle of the PENABLE high period).
PREADY is a signal added to the AMBA 3 APB protocol to allow the peripheral to extend the "ACCESS" phase of the APB transfer, so adding wait states when PREADY is driven low.
PREADY is only considered by the APB master during the ACCESS phase, so outside of this period it will be ignored, hence being shown as high or low at these times.
thanks..for your fast reply..
Can Pready remain high for more than one cycle or it has to go low immediately the next cycle it goes high?
PREADY can remain high forever if you don't want to add wait states. If you are connecting an APB2 peripheral (with no PREADY output) to an APB3 master, you would just tie the PREADY input on the master high.
PREADY is only checked during the "ACCESS" phase of an APB access, so during periods when PSEL is low, or when PSEL is high but PENABLE is low (the transfer "SETUP" phase), PREADY is undefined and could be high.