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FlexBus
Freescale Semiconductor
20-11
20.4.1.1
General Chip-Select Operation
When a bus cycle is routed to the FlexBus, the device first compares its address with the base address and
mask configurations programmed for chip-selects 0 to 5 (configured in CSCR0 – CSCR5). The results
depend on if the address matches or not as shown in
.
20.4.1.2
8-, 16-, and 32-Bit Port Sizing
Static bus sizing is programmable through the port size bits, CSCR[PS]. The processor always drives a
-bit address on the FB_AD bus regardless of the external device’s address size. The external device
must connect its address lines to the appropriate FB_AD bits from FB_AD0 upward. Its data bus must be
connected to FB_AD[7:0] from
downward. No bit ordering is required when connecting
address and data lines to the FB_AD bus. For example, a full 16-bit address/16-bit data device connects
its addr[15:0] to FB_AD[16:1] and data[15:0] to FB_AD[31:16]. See
for a graphical
connection.
20.4.1.3
Global Chip-Select Operation
FB_CS0, the global (boot) chip-select, supports external boot memory accesses before system
initialization. Its operation differs from other external chip-select outputs after system reset.
After system reset, FB_CS0 is asserted for every external access. No other chip-select can be used until
the valid bit, CSMR0[V], is set; at this point FB_CS0 functions as configured. After this, FB_CS[5:1] can
be used as well. At reset during parallel boot, the logic levels on the FB_AD[4:3] signals determine global
chip-select port size. During serial boot, the value of SBF_RCON[127:126] determine the port size.
20.4.2
Data Transfer Operation
Data transfers between the chip and other devices involve these signals:
Table 20-7. Results of Address Comparison
Address Matches
CSAR
n
?
Result
Yes,
one CSAR
The appropriate chip-select is asserted, generating an external bus cycle as defined in the chip-select
control register.
If CSMR[WP] is set and a write access is performed, the internal bus cycle terminates with a bus error,
no chip select is asserted, and no external bus cycle is performed.
No
The chip-select signals are not driven. However, the FlexBus runs an external bus cycle with external
termination.
Yes,
multiple CSARs
The chip-select signals are driven. However, they are driven using an external burst-inhibited bus cycle
with external termination on a 32-bit port.
•
Address/data bus (FB_AD[31:0])
32
FB_AD31
See
Chapter 11, “Chip Configuration Module (CCM),”
for more information.
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 ...