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Bus Operation
MCF5272 ColdFire
®
Integrated Microprocessor User’s Manual, Rev. 3
20-8
Freescale Semiconductor
20.6.1
Interface for FLASH/SRAM Devices with Byte Strobes
CSBR
n
[EBI] is 00 for FLASH/SRAM devices and peripherals having 16- or 32-bit data bus widths. These
memory devices have separate pins for independent byte strobes, write enable, chip select, and output
enable. All chip selects support this EBI mode.
The number of wait states required for the external memory or peripheral is programmed through
CSOR
n
[WS]. The external transfer acknowledge signal, TA, is provided to allow off-chip control of wait
states. External control of wait states is enabled when CSOR
n
[WS] is 0x1F. When TA is used to terminate
the bus cycle, the bus cycle will have a minimum of one wait states. Additional wait states can be added
by delaying the assertion of TA.
Figure 20-3. Longword Read; EBI = 00; 32-Bit Port; Internal Termination
NOTE
Wait states, if needed, are added immediately after C2 in
Table 20-7. External Bus Interface Codes for CSBRs
A0
CSBR
n
[EBI]
Applicable Chip Select
Note
16-/32-bit
SRAM/ROM
00
All
For 16/32 bit wide memory devices with byte strobe inputs.
BS[3:0]
are byte read/write enables in this mode. CSBR0[EBI] = 00 at
reset.
SDRAM
01
CS7/SDCS only
One physical bank of SDRAM consisting of 16–256 Mbit devices.
The CS7/SDCS CSORn[WS] must be set to 0x1F.
Reserved
10
—
—
8-bit
SRAM/ROM
11
All
SRAM/ROM timing for 8 bit wide memory devices without byte
strobe inputs.
BS[3:0]
function as byte write enables in this mode.
SDCLK
A[22:0]
D[31:0]
OE, BS[3:0]
R/W
CSn
C1
C2
(H)
(H)
TA