EVAL-ADF4108EBZ1 Datasheet, PDF (18/20 Pages) Analog Devices – PLL Frequency Synthesizer

ADF4108
INTERFACING
The ADF4108 has a simple SPI-compatible serial interface for
writing to the device. CLK, DATA, and LE control the data
transfer. When LE (latch enable) goes high, the 24 bits that have
been clocked into the input register on each rising edge of CLK
are transferred to the appropriate latch. See Figure 2 for the
timing diagram and Table 5 for the latch truth table.
The maximum allowable serial clock rate is 20 MHz. This
means that the maximum update rate possible for the device is
833 kHz or one update every 1.2 μs. This is certainly more than
adequate for systems that have typical lock times in hundreds of
microseconds.
ADuC812 INTERFACE
Figure 20 shows the interface between the ADF4108 and the
ADuC812 MicroConverter®. Because the ADuC812 is based on
an 8051 core, this interface can be used with any 8051-based
microcontroller. The MicroConverter is set up for SPI master
mode with CPHA = 0. To initiate the operation, the I/O port
driving LE is brought low. Each latch of the ADF4108 needs a
24-bit word. This is accomplished by writing three 8-bit bytes
from the MicroConverter to the device. When the third byte
has been written, the LE input should be brought high to
complete the transfer.
On first applying power to the ADF4108, it needs four writes
(one each to the initialization latch, function latch, R counter
latch, and N counter latch) for the output to become active.
I/O port lines on the ADuC812 are also used to control power-
down (CE input) and to detect lock (MUXOUT configured as
lock detect and polled by the port input).
When operating in the mode described, the maximum
SCLOCK rate of the ADuC812 is 4 MHz. This means that
the maximum rate at which the output frequency can be
changed is 166 kHz.
Data Sheet
SCLOCK
MOSI
ADuC812
I/O PORTS
CLK
DATA
LE _ADF4108
CE
MUXOUT
(LOCK DETECT)
Figure 20. ADuC812 to ADF4108 Interface
ADSP-21xx INTERFACE
Figure 21 shows the interface between the ADF4108 and the
ADSP-21xx digital signal processor. The ADF4108 needs a
24-bit serial word for each latch write. The easiest way to
accomplish this using the ADSP-21xx family is to use the
autobuffered transmit mode of operation with alternate
framing. This provides a means for transmitting an entire block
of serial data before an interrupt is generated. Set up the word
length for 8 bits and use three memory locations for each 24-bit
word. To program each 24-bit latch, store the three 8-bit bytes,
enable the autobuffered mode, and then write to the transmit
register of the DSP. This last operation initiates the autobuffer
transfer.
SCLOCK
MOSI
ADSP-21xx ^TFS
I/O FLAGS
CLK
DATA
LE _ADF4108
CE
MUXOUT
(LOCK DETECT)
Figure 21. ADSP-21xx to ADF4108 Interface
Rev. B | Page 18 of 20