A.1. AMBA APB signals

The PrimeCell SCI is connected to the AMBA APB bus as a bus slave. With the exception of the BnRES signal, the APB signals have a P prefix and are active HIGH. Active LOW signals contain a lower case n. The AMBA APB signals are described in Table A.1.

Table A.1. AMBA APB signal descriptions

NameType

Source/

destination

Description
BnRESInputReset controllerBus reset signal, active LOW.
PADDR[7:2]InputAPB bridgeSubset of AMBA APB address bus.
PCLKInputClock generatorAMBA APB clock, used to time all bus transfers.
PENABLEInputAPB bridgeAMBA APB enable signal. PENABLE is asserted HIGH for one cycle of PCLK to enable a bus transfer.
PRDATA [15:0]OutputAPB bridgeSubset of unidirectional AMBA APB read data bus.
PSELInputAPB bridgePrimeCell SCI select signal from decoder. When HIGH this signal indicates the slave device is selected by the APB bridge, and that a data transfer is required.
PWDATA [15:0]InputAPB bridgeSubset of unidirectional AMBA APB write data bus.
PWRITEInputAPB bridgeAMBA APB transfer direction signal, indicates a write access when HIGH, read access when LOW.
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