AD9953ASV datasheet(24/42 Pages) AD

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PRELIMINARY TECHNICAL DATA

AD9953

Similarly, when the RAM output drives the phase offset adder the Frequency Tuning Word (FTW,

hex address 04h) drives the phase accumulator. When CFR1<31> is logic zero, the RAM is

inactive unless being written to via the serial port. The power up state of the AD9953 is single

tone mode, in which the RAM Enable bit is inactive. The RAM is segmented into four unique

slices controlled by the Profile<1:0> input pins.

All RAM writes/reads, unless otherwise specified, are controlled by the Profile<1:0> input pins

and the respective RAM Segment Control Word. The RAM can be written to during normal

operation BUT any IO operation that commands the RAM to be written immediately suspends read

operation from the RAM, causing the current mode of operation to be non-functional. This

excludes single tone mode, as the RAM is not read in this mode.

Modes of Operation

Single Tone Mode

In single tone mode, the DDS core uses a single tuning word. Whatever value is stored in FTW0 is

supplied to the phase accumulator. This value can only be changed statically, which is done by

writing a new value to FTW0 and issuing an I/O UPDATE. Phase adjustment is possible through

the phase offset register.

RAM Controlled Modes of Operation

Direct Switch Mode

Direct Switch Mode enables FSK or PSK modulation. The AD9953 is programmed for Direct

Switch Mode by writing the RAM Enable bit true and programming the RAM Segment Mode

Control bits of each desired profile to logic 000(b). This mode simply reads the RAM contents at

the RAM Segment Beginning Address for the current profile. No address ramping is enabled in

Direct Switch mode.

To perform 4-tone FSK, the user programs each RAM Segment Control Word for Direct Switch

Mode and a unique beginning address value. In addition, the RAM Enable bit is written true which

enables the RAM and the RAM destination bit is written false, setting the RAM output to be the

frequency tuning word. The Profile<1:0> inputs are the 4-tone FSK data inputs. When the profile

is changed, the frequency tuning word stored in the new profile is loaded into the phase

accumulator and used to increment the currently stored value in a phase continuous fashion. The

Phase Offset Word drives the phase-offset adder. 2-tone FSK is accomplished by using only one

Profile pin for data.

Programming the AD9953 for PSK modulation is similar to FSK except the RAM destination bit is

set to a logic 1, enabling the RAM output to drive the phase offset adder. The FTW drives the

input to the phase accumulator. Toggling the profile pins changes (modulates) the current phase

REV. PrB 1/30/03

Page 24

Analog Devices, Inc.

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