
10-2
MCF5249UM
MOTOROLA
MCF5249Chip-Select Operation
IDE-DIOR and IDE-DIOW can also be used as enables to access an IDE drive or another AT-bus
peripheral. This added functionality allows users to insert more than 16 wait states on IDE-DIOR,
IDE-DIOW, and allows dynamic cycle termination using the IORDY signal.
10.2.1.4 CS3/SRE/GPIO11 AND SWE/GPIO12
These two signals go active during CS3 cycles. SRE can be programmed to go active on read and write
cycles, or SRE can be programmed to go active only on read cycles, and SWE only on write cycles. It has
identical features as the normal CS3. It can be programmed for an address location as well as for masking,
port size and burst capability indication, wait state generation, and internal/external termination.
Note: The SWE and SRE signals are only used on the 160 MAPBGA package.
SRE and SWE can also be used as enables to access an IDE drive or another AT-bus peripheral. This
added functionality allows users to insert more than 16 wait states on SRE, SWE, and allows dynamic
cycle termination using the IORDY signal.
10.2.2
OUTPUT ENABLE OE/GPIO9
The OE/GPIO9 signal interfaces memory and/or peripherals to enable a read transfer. It is asserted and
negated on the falling edge of the clock. This signal is asserted only when there is a match of one of the
chip selects for the current address decode.
10.2.3
BUFFER ENABLE SIGNALS - BUFENB1 AND BUFENB2
The BUFENB1/GPIO57 and BUFENB2/GPIO17 signals are intended to enable bus buffers sitting between
some chip select modules and the MCF5249 bus. BUFENB1 is always active on CS0, BUFENB2 is always
inactive on CS0. It is programmable if the bus buffer signals go active on CS1, CS2, and CS3.
Note: The BUFENB2 signal is only used in the 160 MAPBGA package.
10.2.4
IORDY - BUS TERMINATION SIGNAL
The IORDY signal controls the insertion of wait states on the third and fourth chip select.
10.3
MCF5249CHIP-SELECT OPERATION
10.3.1
CHIP-SELECT MODULE
The chip select module provides a glueless interface to many types of external memory. The module
contains the necessary external control signals to interface to SRAM, PROM, EPROM, EEPROM, FLASH
and peripherals.
Some features of the chip selects are controlled by the IDECONFIG1 and IDECONFIG2 registers. These
Each of the four chip select outputs has an associated mask register and control register.
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Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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