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Signal Description
MCF5253 Reference Manual, Rev. 1
Freescale Semiconductor
2-7
2.5
Chip Selects
There are three chip select outputs on the MCF5253 device. CS0/CS4 and CS1/QSPI_CS3/GPIO28 and
CS2 which is associated with the IDE interface read and write strobes—IDE_DIOR and IDE_DIOW.
CS0 and CS4 are multiplexed. The MCF5253 has the option to boot from an internal Boot Rom.
The function of the CS0/CS4 pin is determined by the boot mode. When the device is booted from internal
ROM, the internal ROM is accessed with CS0 (required for boot) and the CS0/CS4 pin is driven by CS4.
When the device is booted from external ROM / Flash, the CS0/CS4 pin is driven by CS0 and the internal
ROM is disabled.
The active low chip selects can be used to access asynchronous memories. The interface is glueless.
2.6
ISA Bus
The MCF5253 supports an ISA bus. Using the ISA bus protocol, reads and writes for one ISA bus
peripheral is possible. IDE_DIOR/GPIO31 and IDE_DIOW/GPIO32 are the read and write strobe. The
peripheral can insert wait states by pulling IDE_IORDY/GPIO33.
CS2 is associated with the IDE_DIOR and IDE_DIOW.
2.7
Bus Buffer Signals
As the MCF5253 has a quite complicated slave bus, with the possibility of having DRAM, asynchronous
memories and an ISA peripherals on the bus, it may become necessary to introduce a buffer on the bus.
The MCF5253 has a glueless interface to steer these bus buffers with 2 bus buffer output signals
BUFENB1/GPIO29 and BUFENB2/GPIO30.
2.8
I
2
C Module Signals
There are two I
2
C interfaces on this device.
The I
2
C module acts as a two-wire, bidirectional serial interface between the MCF5253 processor and
peripherals with an I
2
C interface (e.g., LED controller, A-to-D converter, D-to-A converter). When
devices connected to the I
2
C bus drive the bus, they will either drive logic-0 or high-impedance. This can
be accomplished with an open-drain output.
Synchronous DRAM clock
The DRAM clock is driven by the BCLK/GPIO40 signal.
Synchronous DRAM clock enable
The BCLKE active high output signal is used during synchronous mode to route
directly to the SCKE signal of external SDRAMs. This signal provides the clock
enable to the SDRAM.
Table 2-2. SDRAM Controller Signals
SDRAM Signal
Description
Содержание MCF5253
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