AMBA Design Kit Technical Reference Manual - ARM Information ...

APB Components4.2 Example APB slaveThe example APB slave, EgApbSlave, provides sample HDL code, that can be used as abasis for further enhancement, to produce a slave on the APB. Figure 4-4 shows that theexample APB slave consists of five functional blocks contained within one top-levelentity.Valid transferdetect logicRead datagenerationlogicStandardAPBslaveinterfaceIdentificationregistersRegisterupdate enablelogic4 x 32-bitregistersFigure 4-4 Example APB slave componentsThe example APB slave includes the following features:• A simple APB slave interface.• System bus clock and reset, that are synchronous between AHB and APBdomains.• 32-bit data bus, endian-independent, but data handling is 32-bits only.• Data transfers require two clock cycles.• 32-bit address bus.• Four 32-bit registers to hold the write data. Registers can also be read.• Seven read-only locations that return logical functions of the registered write data.4.2.1 Programmer’s modelThe slave only responds to a transfer when not in reset, PRESETn HIGH, and whenPSEL is HIGH and PENABLE is LOW at the time of a rising edge on PCLK. Thetiming of the slave corresponds to the APB specification.ARM DDI 0243C Copyright © 2003, 2007 ARM Limited. All rights reserved. 4-9