
MCF5249Chip-Select Operation
MOTOROLA
Chip-Select Module
10-3
Chip selects (CS0, CS1/GPIO1, DIOR/DIOW (CS2), SRE/SWE(CS3)):
Each has a 16-bit base address register.
Each has a 32-bit mask register, which provides 16-bit address masking and access control.
Each has a 16-bit control register, which provides port size and burst capability indication, wait state
generation, and automatic acknowledge generation features.
Note: The SWE and SRE signals are only used on the 160 MAPBGA package.
Chip select 0 provides special functionality. It is a “global” chip select after reset and provides relocatable
boot ROM capability.
In addition to the 2 external chip select outputs, the module contains 2 chip selects (CS2 and CS3) for use
with AT-bus peripherals such as IDE drives and Flash Card interfaces. Capabilities for CS2 and CS3 are
like CS1, but there are some enhancements for typical AT-bus features. The enhancements are described
10.3.1.1 GENERAL CHIP SELECT OPERATION
The general-purpose chip selects are controlled by the chip select mask register (CSMR), the chip select
control register (CSCR), and by the chip select address register (CSAR). There is one CSAR, CSMR, and
CSCR for each of the chip selects (CS0–CS3).
Chip Selects (CS[3:0]):
The chip select address register controls the base address space of the chip select.
The chip select mask register controls the memory block size and addressing attributes of the chip
select.
The chip select control register programs the features of the chip select signals.
The MCF5249 processor compares the address and mask in CS[3:0] control registers. If the address and
attributes do not match in a single chip select register, the cycle will terminate in error.
Table 10-1 shows
the type of access depending on what matches are made in the CS control registers.
Table 10-1 Accesses by Matches in CS Control Registers
NUMBER OF CHIP
SELECTS REGISTER
MATCHES
TYPE OF ACCESS
None
Error1
Single
As defined by chip select
control register
Multiple
External2,3
Note 1: The cycle will not terminate, and the bus will hang.
Watchdog timer may recover from hung bus.
Note 2: External termination by pulling the TA pin low is
required. Glueless interface with memory is not
possible. If TA pin is not pulled low, cycle will not
terminate causing the bus to hang.
Note 3: For the case of multiple chip selects matching, all of
the matching chip selects will be asserted.
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Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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