ADF4252BCPZ-R7 datasheet(28/30 Pages) AD

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ADF4252

Data Sheet

Rev. E | Page 28 of 30

INTERFACING

The ADF4252 has a simple SPI-compatible serial interface for

writing to the device. SCLK, SDATA, and LE control the data

transfer. When LE (latch enable) goes high, the 24 bits that were

clocked into the input register on each rising edge of SCLK are

transferred to the appropriate latch. See Figure 2 for the timing

diagram and Table 5 for the control bit truth table.

The maximum allowable serial clock rate is 20 MHz, which

means that the maximum update rate possible for the device is

833 kHz or one update every 1.2 μs. This is more than adequate

for systems that have typical lock times in hundreds of

microseconds.

ADuC812 INTERFACE

Figure 42 shows the interface between the ADF4252 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

input/output port driving LE is brought low. Each latch of the

ADF4252 needs (at most) 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 must

be brought high to complete the transfer.

The input/output 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.

ADuC812

ADF4252

SCLK

SDATA

MUXOUT

(LOCK DETECT)

SCLOCK

MOSI

I/O PORTS

Figure 42. ADuC812 to ADF4252 Interface

ADSP-2181 INTERFACE

Figure 43 shows the interface between the ADF4252 and the

ADSP-2181 digital signal processor. Each latch of the ADF4252

needs (at most) a 24-bit word. The easiest way to accomplish

this using the ADSP-2181 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 eight 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.

ADSP-2181

ADF4252

SCLK

SDATA

MUXOUT

(LOCK DETECT)

SCLK

I/O FLAGS

TFS

Figure 43. ADSP-2181 to ADF4252 Interface

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