
13-2
MCF5249UM
MOTOROLA
memory is connected. The IDE and SmartMedia interfaces share most signals with the ColdFire address
and data bus. The “second” bus buffer prevents the flash ROM signals from going to/from IDE and
SmartMedia interfaces.
To support this bus set-up, a number of signals are available.
BUFENB1: active-low external buffer enable. This enable is always active when CS0 is active, and
should enable a buffer going to the boot ROM.
BUFENB2: active-low external buffer enable. This enable is always inactive when CS0 is active,
and should enable a buffer for peripheral devices, except boot ROM.
IDE-DIOR, IDE-DIOW: active-low IDE bus read and write strobe.
IDE-IORDY: active-high “ready” indication from IDE device to MCF5249.
SRE, SWE: active-low SmartMedia read and write strobe
Note: The SWE and SRE signals are only used on the 160 MAPBGA package.
The extra bus signals, and their configuration are detailed in the following section.
13.1.1
BUFFER ENABLES BUFENB1, BUFENB2, AND ASSOCIATED LOGIC.
Buffer enables BUFENB1 and BUFENB2 allow a seamless interface to external bus buffers. The buffers
may be placed on the address and the data bus.
Figure 13-2 Buffer Enables (BUFENB1 and BUFENB2)
BUFENB1 is always active on CS0. BUFENB2 is never active on CS0. Either of the buffer enables can be
programmed to be active on CS1, CS2, or CS3.
BUFENB1 and BUFENB2 will go active at time CSPRE
before the falling edge of the Chip Select signal, and continue to be active for a time CSPOST after the
rising edge of the chip select signal. The pre-drive time
CSPRE is realized by delaying the falling edge of
the select signal. If pre-drive time
CSPRE is programmed non-zero, and internal ColdFire cycle
termination is used, chip select length will be
CSPRE shorter than the programmed length. Times
CSPRE, CSPOST are the same for both BUFENB1 AND BUFENB2. Times CSPRE,
CSPOST are independently programmable for every select.
Buffer enable configuration is programmable using the
IDE_CONFIG1 register.
BUFENBx
CSPRE
CSPOST
CSx_core
bufenx_b
cspre
CS0, CS1,
DIOR, DIOW, SRE, SWE
cspost
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Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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