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FlexBus
Freescale Semiconductor
20-9
19–18
RDAH
Read address hold or deselect. This field controls the address and attribute hold time after the termination during a
read cycle that hits in the chip-select address space.
Note:
The hold time applies only at the end of a transfer. Therefore, during a burst transfer or a transfer to a port size
smaller than the transfer size, the hold time is only added after the last bus cycle.
The number of cycles the address and attributes are held after FB_CS
n
negation depends on the value of
CSCR
n
[AA] as shown below.
17–16
WRAH
Write address hold or deselect. This field controls the address, data, and attribute hold time after the termination of
a write cycle that hits in the chip-select address space.
Note:
The hold time applies only at the end of a transfer. Therefore, during a burst transfer or a transfer to a port size
smaller than the transfer size, the hold time is only added after the last bus cycle.
00 Hold address and attributes one cycle after FB_CS
n
negates on writes. (Default FB_CS
n
)
01 Hold address and attributes two cycles after FB_CS
n
negates on writes.
10 Hold address and attributes three cycles after FB_CS
n
negates on writes.
11 Hold address and attributes four cycles after FB_CS
n
negates on writes. (Default FB_CS0)
15–10
WS
Wait states. The number of wait states inserted after FB_CS
n
asserts and before an internal transfer acknowledge
is generated (WS = 0 inserts zero wait states, WS = 0x3F inserts 63 wait states). If AA is reserved, FB_TA must be
asserted by the external system regardless of the number of generated wait states. In that case, the external transfer
acknowledge ends the cycle. An external FB_TA supersedes the generation of an internal FB_TA.
9
Reserved, must be cleared.
8
AA
Auto-acknowledge enable. Determines the assertion of the internal transfer acknowledge for accesses specified by
the chip-select address.
0 No internal FB_TA is asserted. Cycle is terminated externally
1 Internal transfer acknowledge is asserted as specified by WS
Note:
If AA is set for a corresponding FB_CS
n
and the external system asserts an external FB_TA before the
wait-state countdown asserts the internal FB_TA, the cycle is terminated. Burst cycles increment the address
bus between each internal termination.
7–6
PS
Port size. Specifies the data port width associated with each chip-select. It determines where data is driven during
write cycles and where data is sampled during read cycles.
00 32-bit port size. Valid data sampled and driven on FB_D[31:0]
01 8-bit port size. Valid data sampled and driven on FB_D[31:24]
1
x
16-bit port size. Valid data sampled and driven on FB_D[31:16]
Table 20-6. CSCR
n
Field Descriptions (Continued)
Field
Description
RDAH
AA = 0
AA = 1
00
(FB_CS
n
Default)
1 cycle
0 cycles
01
2 cycles
1 cycles
10
3 cycles
2 cycles
11
(FB_CS0 Default)
4 cycles
3 cycles
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 ...