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FlexBus
Freescale Semiconductor
20-27
The FlexBus can support 2-1-1-1 burst cycles to maximize system performance. Delaying termination of
the cycle can add wait states. If internal termination is used, different wait state counters can be used for
the first access and the following beats.
The CSCR
n
registers enable bursting for reads, writes, or both. Memory spaces can be declared
burst-inhibited for reads and writes by clearing the appropriate CSCR
n
[BSTR,BSTW] bits.
shows a longword read to an 8-bit device programmed for burst enable. The transfer results
in a 4-beat burst and the data is driven on
The transfer size is driven at longword (00)
throughout the bus cycle.
NOTE
In non-multiplexed address/data mode, the address on FB_A increments
only during internally-terminated burst cycles. The first address is driven
throughout the entire burst for externally-terminated cycles.
Figure 20-25. Longword-Read Burst from 8-Bit Port 2-1-1-1 (No Wait States)
shows a longword write to an 8-bit device with burst enabled. The transfer results in a 4-beat
burst and the data is driven on
The transfer size is driven at longword (00) throughout the
bus cycle.
NOTE
The first beat of any write burst cycle has at least one wait state. If the bus
cycle is programmed for zero wait states (CSCR
n
[WS] = 0), one wait state
is added. Otherwise, the programmed number of wait states are used.
FB_AD[31:24].
In multiplexed address/data mode, the address is driven on FB_AD only
during the first cycle for internally- and externally-terminated cycles.
FB_CLK
FB_R/W
FB_ALE
S0
S1
S2
S2
S2
S2
S3
DATA
DATA
DATA
FB_TSIZ[1:0]
00
DATA
DATA
DATA
DATA
DATA
ADDR + 1
ADDR + 2
ADDR + 3
Mux’d Bus
Non-Mux’d Bus
FB_A[23:0]
ADDR[23:0]
ADDR[23:0]
FB_D[31:24]
ADDR[31:24]
ADDR[31:24]
FB_AD[23:0]
FB_AD[31:24]
FB_CS
n
, FB_OE
FB_BE/BWE
n,
FB_TBST
FB_TA
S0
FB_AD[31:24].
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 ...