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FlexBus
20-10
Freescale Semiconductor
20.4
Functional Description
20.4.1
Chip-Select Operation
Each chip-select has a dedicated set of registers for configuration and control:
•
Chip-select address registers (CSAR
n
) control the base address space of the chip-select. See
Section 20.3.1, “Chip-Select Address Registers (CSAR0 – CSAR5).”
•
Chip-select mask registers (CSMR
n
) provide 16-bit address masking and access control. See
Section 20.3.2, “Chip-Select Mask Registers (CSMR0 – CSMR5).”
•
Chip-select control registers (CSCR
n
) provide port size and burst capability indication, wait-state
generation, address setup and hold times, and automatic acknowledge generation features. See
Section 20.3.3, “Chip-Select Control Registers (CSCR0 – CSCR5).”
FB_CS0 is a global chip-select after reset and provides external boot memory capability.
5
BEM
Byte-enable mode. Specifies the byte enable operation. Certain memories have byte enables that must be asserted
during reads and writes. BEM can be set in the relevant CSCR to provide the appropriate mode of byte enable
support for these SRAMs.
0 FB_BE/BWE is not asserted for reads. FB_BE/BWE is asserted for data write only.
1 FB_BE/BWE is asserted for read and write accesses.
4
BSTR
Burst-read enable. Specifies whether burst reads are used for memory associated with each FB_CS
n
.
0 Data exceeding the specified port size is broken into individual, port-sized, non-burst reads. For example, a
longword read from an 8-bit port is broken into four 8-bit reads.
1 Enables data burst reads larger than the specified port size, including longword reads from 8- and 16-bit ports,
word reads from 8-bit ports, and line reads from 8, 16-, and 32-bit ports.
3
BSTW
Burst-write enable. Specifies whether burst writes are used for memory associated with each FB_CS
n
.
0 Break data larger than the specified port size into individual, port-sized, non-burst writes. For example, a longword
write to an 8-bit port takes four byte writes.
1 Enables burst write of data larger than the specified port size, including longword writes to 8 and 16-bit ports, word
writes to 8-bit ports, and line writes to 8-, 16-, and 32-bit ports.
2–0
Reserved, must be cleared.
Table 20-6. CSCR
n
Field Descriptions (Continued)
Field
Description
Summary of Contents for MCF54455
Page 33: ...xxviii Freescale Semiconductor ...
Page 67: ...Freescale Semiconductor 1 ...
Page 125: ...Freescale Semiconductor 1 ...
Page 145: ...Enhanced Multiply Accumulate Unit EMAC 5 21 Freescale Semiconductor ...
Page 173: ...Cache 6 28 Freescale Semiconductor ...
Page 179: ...Static RAM SRAM 7 6 Freescale Semiconductor ...
Page 207: ...Power Management 9 16 Freescale Semiconductor ...
Page 323: ...Reset Controller Module 13 8 Freescale Semiconductor ...
Page 389: ...Pin Multiplexing and Control 16 44 Freescale Semiconductor ...
Page 575: ...PCI Bus Controller 22 58 Freescale Semiconductor ...
Page 600: ...Advanced Technology Attachment ATA Freescale Semiconductor 23 25 ...
Page 601: ...Freescale Semiconductor 1 ...
Page 842: ...I2 C Interface Freescale Semiconductor 33 16 ...
Page 843: ...Freescale Semiconductor 1 ...
Page 921: ...Revision History A 6 Freescale Semiconductor ...