
10-4
MCF5249UM
MOTOROLA
Programming Model
10.3.1.1.1 PORT SIZING
The MCF5249 only supports a 16-wide port size (PS). The size of the port controlled by a chip-select is
programmable. The port size is specified by the (PS) bits in the chip select control register (CSCR). It
should always be programmed as a 16-wide port. See
Section 10.4.2.3 for details.
10.3.2
GLOBAL CHIP-SELECT OPERATION
CS0 is the global (boot) chip select and it allows address decoding for the boot ROM before system
initialization occurs. Its operation differs from the other external chip-select outputs following a system
reset.
After system reset, CS0 is asserted for every external access. Internal accesses can be made to go
external by setting the internal bus arbitration control (IARBCTRL) bit of the default bus master (MPARK)
register in the system integration module (SIM). No other chip-select can be used while CS0 is a global
chip select. CS0 operates in this manner until the valid bit is set in chip select mask register CSMR0[0], at
which point CS1 may be used. At reset, the port size and automatic acknowledge functions of the global
chip-select are determined.
The reset value is always auto-acknowledge (AA) with 15 wait states, and the port size bits (PS[1:0]) in
CSCR0 are set to “10”, 16 bit port.
Provided the required address range is first loaded into chip select address register (CSAR), CS0 can be
programmed to continue to decode for a range of addresses after the valid (V) bit is set. After the V-bit is
set for CS0, global chip-select can be restored only with another system reset.
10.4
PROGRAMMING MODEL
10.4.1
CHIP-SELECT REGISTERS MEMORY MAP
Table 10-2 shows the memory map of all the chip-select registers. Reading reserved locations returns
zeros.
Similarly, the CSCRs should be accessed through a MOV.L to longword address offset they belong to,
while reading and writing to the lower 16-bits of the longword data transfer (DATA[15:0]).
Note: All of these accesses are longword in length, instead of word length, even though
both the CSARs and CSCRs use only 16 bits in the 32-bits registers.
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Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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