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Serial Boot Facility (SBF)
12-4
Freescale Semiconductor
12.4
Functional Description
When enabled, the SBF inserts three additional steps into the normal system boot process:
•
Serial initialization and shift clock frequency adjustment
•
Reset configuration and optional boot load
•
Execution transfer
12.4.1
Serial Initialization and Shift Clock Frequency Adjustment
The following sequence is followed during a serial boot sequence:
1. The SBF is engaged when BOOTMOD[1:0] = 11 concurrent with the release of a pending source
of reset (power-on, software watchdog, RESET pin, etc.).
2. Boot-up is paused.
3. The weak internal pull-up on SBF_DI is enabled. This allows a 1-to-0 transition to register when
the SPI memory output switches from high-impedance to logic 0.
4. The SBF shifts the standard SPI memory read command (0x03) followed by repeated 0x00 address
bytes to the SPI memory at
f
REF
60.
3–0
BLDIV
Boot loader clock divider. Determines the SBF clock (PLL input reference clock) divisor that generates the serial shift
clock output on SBF_CK. Prior to the serial boot sequence, a divisor of 67 is used.
During the serial boot sequence, this field is loaded with the value read from the SPI memory. The application may
write to this register to change the divisor for any subsequent serial boot that follows a soft-reset condition.
Because this register is write-once, the application must write the value for this field in the same write that the FR bit
is written (regardless of the value written to the FR bit). Any subsequent writes to this field prior to a power-on reset
event terminate without effect.
Table 12-4. SBFCR Field Descriptions (continued)
Field
Description
BLDIV
Ideal
Divisor
Shift Clock
BLDIV
Ideal
Divisor
Shift Clock
High Time
(f
ref
Ticks)
Low Time
(f
ref
Ticks)
High Time
(f
ref
Ticks)
Low Time
(f
ref
Ticks)
0000
1
Bypass
Bypass
1000
14
7
7
0001
2
1
1
1001
17
9
8
0010
3
2
1
1010
25
13
12
0011
4
2
2
1011
33
17
16
0100
5
3
2
1100
34
17
17
0101
7
4
3
1101
50
25
25
0110
10
5
5
1110
67
34
33
0111
13
7
6
1111
Reserved
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 ...