Datasheet

Rev. I | Page 14 of 64 | August 2013
ADSP-BF531/ADSP-BF532/ADSP-BF533
As shown in Figure 9, the core clock (CCLK) and system
peripheral clock (SCLK) are derived from the input clock
(CLKIN) signal. An on-chip PLL is capable of multiplying the
CLKIN signal by a user programmable 0.5 to 64 multiplica-
tion factor (bounded by specified minimum and maximum
VCO frequencies). The default multiplier is 10, but it can be
modified by a software instruction sequence. On-the-fly
frequency changes can be effected by simply writing to the
PLL_DIV register.
All on-chip peripherals are clocked by the system clock (SCLK).
The system clock frequency is programmable by means of the
SSEL3–0 bits of the PLL_DIV register. The values programmed
into the SSEL fields define a divide ratio between the PLL output
(VCO) and the system clock. SCLK divider values are 1 through
15. Table 6 illustrates typical system clock ratios.
The maximum frequency of the system clock is f
SCLK
. The divi-
sor ratio must be chosen to limit the system clock frequency to
its maximum of f
SCLK
. The SSEL value can be changed dynami-
cally without any PLL lock latencies by writing the appropriate
values to the PLL divisor register (PLL_DIV). When the SSEL
value is changed, it affects all of the peripherals that derive their
clock signals from the SCLK signal.
The core clock (CCLK) frequency can also be dynamically
changed by means of the CSEL1–0 bits of the PLL_DIV register.
Supported CCLK divider ratios are 1, 2, 4, and 8, as shown in
Table 7. This programmable core clock capability is useful for
fast core frequency modifications.
BOOTING MODES
The ADSP-BF531/ADSP-BF532/ADSP-BF533 processors have
two mechanisms (listed in Table 8) for automatically loading
internal L1 instruction memory after a reset. A third mode is
provided to execute from external memory, bypassing the boot
sequence.
The BMODE pins of the reset configuration register, sampled
during power-on resets and software-initiated resets, imple-
ment the following modes:
• Execute from 16-bit external memory – Execution starts
from address 0x2000 0000 with 16-bit packing. The boot
ROM is bypassed in this mode. All configuration settings
are set for the slowest device possible (3-cycle hold time;
15-cycle R/W access times; 4-cycle setup).
• Boot from 8-bit or 16-bit external flash memory – The flash
boot routine located in boot ROM memory space is set up
using asynchronous Memory Bank 0. All configuration set-
tings are set for the slowest device possible (3-cycle hold
time; 15-cycle R/W access times; 4-cycle setup).
• Boot from SPI serial EEPROM/flash (8-, 16-, or 24-bit
addressable, or Atmel AT45DB041, AT45DB081, or
AT45DB161) – The SPI uses the PF2 output pin to select a
single SPI EEPROM/flash device, submits a read command
and successive address bytes (0x00) until a valid 8-, 16-, or
24-bit addressable EEPROM/flash device is detected, and
begins clocking data into the processor at the beginning of
L1 instruction memory.
• Boot from SPI serial master – The Blackfin processor oper-
ates in SPI slave mode and is configured to receive the bytes
of the LDR file from an SPI host (master) agent. To hold off
the host device from transmitting while the boot ROM is
busy, the Blackfin processor asserts a GPIO pin, called host
wait (HWAIT), to signal the host device not to send any
Figure 9. Frequency Modification Methods
Table 6. Example System Clock Ratios
Signal Name
SSEL3–0
Divider Ratio
VCO/SCLK
Example Frequency Ratios
(MHz)
VCO SCLK
0001 1:1 100 100
0101 5:1 400 80
1010 10:1 500 50
PLL
0.5u
to 64u
÷1to15
÷1,2,4,8
VCO
CLKIN
“FINE” ADJUSTMENT
REQUIRES PLL SEQUENCING
“COARSE” ADJUSTMENT
ON-THE-FLY
CCLK
SCLK
SCLK d CCLK
SCLK d
133 MHz
Table 7. Core Clock Ratios
Signal Name
CSEL1–0
Divider Ratio
VCO/CCLK
Example Frequency Ratios
(MHz)
VCO CCLK
00 1:1 300 300
01 2:1 300 150
10 4:1 400 100
11 8:1 200 25
Table 8. Booting Modes
BMODE1–0 Description
00 Execute from 16-bit external memory (bypass
boot ROM)
01 Boot from 8-bit or 16-bit FLASH
10 Boot from serial master connected to SPI
11 Boot from serial slave EEPROM/flash (8-,16-, or 24-
bit address range, or Atmel AT45DB041,
AT45DB081, or AT45DB161serial flash)