Memory Controller

asserted on writes to Variable Latency I/O devices, and nWE is asserted on writes to all other static devices, both synchronous and asynchronous. For SRAM and variable latency I/O, DQM[3:0] are byte selects for both reads and writes.

When the processor comes out of reset, it starts fetches and executes instructions at address 0x00, which corresponds to memory selected by nCS<0>. The boot ROM must be located at this address. The BOOT_SEL pins determine the type of boot memory (refer to Section 6.10.1).

6.2.316-Bit PC Card / Compact Flash Interface

The processor card interface is based on The PC Card Standard - Volume 2 - Electrical Specification, Release 2.1, and CF+ and CompactFlash Specification Revision 1.4. The 16-bit PC Card/Compact Flash interface provides control signals to support any combination of 16-bit PC Card/Compact Flash for two card sockets, using address line (MA[25:0]) and data lines (MD[15:0]).

The processor 16-bit PC Card / Compact Flash Controller provides the following signals.

nPREG is muxed with MA[26] and selects register space (I/O or attribute) versus memory space

nPOE and nPWE allow memory and attribute reads and writes

nPIOR, nPIOW, and nIOIS16 control I/O reads and writes

nPWAIT allows extended access times

nPCE2 and nPCE1 are byte select high and low for a 16-bit data bus

PSKTSEL selects between two card sockets

6.3Memory System Examples

This section provides examples of memory configurations that are possible with the processor. Figure 6-2shows a system that uses 1M x 16-bit x 4-bank SDRAM devices for a total of

48 Mbytes.

6-4

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Intel PXA255 manual Memory System Examples, 3 16-Bit PC Card / Compact Flash Interface