AD9953_17 datasheet(16/32 Pages) AD

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AD9953

Data Sheet

Rev. B | Page 16 of 32

Control Register Bit Descriptions

Control Function Register. No. 1 (CFR1)

The CFR1 is used to control the various functions, features, and

modes of the AD9953. The functionality of each bit is below.

CFR1<31>: RAM Enable Bit

CFR1<31> = 0 (default). The RAM is powered down to

conserve power. Single-tone mode of operation is active.

CFR1<31> = 1. If CFR1<31> is active, the RAM is enabled for

operation. Access control for normal operation is controlled via

the mode control bits of the RSCW for the current profile.

CFR1<30>: RAM Destination Bit

CFR1<30> = 0 (default). If CFR1<31> is active, a Logic 0 on the

RAM destination bit (CFR1<30> = 0) configures the AD9953

such that the RAM output drives the phase accumulator (i.e.,

the frequency tuning word). If CFR1<31> is inactive,

CFR1<30> is a Don’t Care.

CFR1<30> = 1. If CFR1<31> is active, a Logic 1 on the RAM

destination bit (CFR1<30> = 1) configures the AD9953 such

that the RAM output drives the phase-offset adder (i.e., sets the

phase offset of the DDS core).

CFR1<29:27>: Not Used

CFR1<26>: Amplitude Ramp Rate Load Control Bit

CFR1<26> = 0 (default). The amplitude ramp rate timer is

loaded only upon timeout (timer == 1) and is not loaded due to

an I/O UPDATE input signal.

CFR1<26> = 1. The amplitude ramp rate timer is loaded upon

timeout (timer == 1) or at the time of an I/O UPDATE input signal.

CFR1<25>: Shaped On-Off Keying Enable Bit

CFR1<25> = 0 (default). Shaped on-off keying is bypassed.

CFR1<25> = 1. Shaped on-off keying is enabled. When enabled,

CFR1<24> controls the mode of operation for this function.

CFR1<24>: Auto Shaped On-Off Keying Enable Bit (Only Valid

when CFR1<25> Is Active High)

CFR1<24> = 0 (default). When CFR1<25> is active, a Logic 0

on CFR1<24> enables the manual shaped on-off keying

operation. Each amplitude sample sent to the DAC is multiplied

by the amplitude scale factor. See the Shaped On-Off Keying

section for details.

CFR1<24> = 1. When CFR1<25> is active, a Logic 1 on

CFR1<24> enables the auto shaped on-off keying operation.

Toggling the OSK pin high will cause the output scalar to ramp

up from zero scale to the amplitude scale factor at a rate deter-

mined by the amplitude ramp rate. Toggling the OSK pin low

will cause the output to ramp down from the amplitude scale

factor to zero scale at the amplitude ramp rate. See the Shaped

On-Off Keying section for details.

CFR1<23>: Automatic Synchronization Enable Bit

CFR1<23> = 0 (default). The automatic synchronization feature

of multiple AD9953s is inactive.

CFR1<23> = 1. The automatic synchronization feature of

multiple AD9953s is active. The device will synchronize its

internal synchronization clock (SYNC_CLK) to align to the

signal present on the SYNC_IN input. See the Synchronizing

Multiple AD9953s section for details.

CFR1<22>: Software Manual Synchronization of Multiple

AD9953s

CFR1<22> = 0 (default). The manual synchronization feature is

inactive.

CFR1<22> = 1. The software controlled manual synchroniza-

tion feature is executed. The SYNC_CLK rising edge is

advanced by one SYNC_CLK cycle and this bit is cleared. To

advance the rising edge multiple times, this bit needs to be set

for each advance. See the Synchronizing Multiple AD9953s

section for details.

CFR1<21:14>: Not Used

CFR1<13>: Auto-Clear Phase Accumulator Bit

CFR1<13> = 0 (default). The current state of the phase accumula-

tor remains unchanged when the frequency tuning word is applied.

CFR1<13> = 1. This bit automatically synchronously clears

(loads 0s into) the phase accumulator for one cycle upon

reception of an I/O UPDATE signal.

CFR1<12>: Sine/Cosine Select Bit

CFR1<12> = 0 (default). The angle-to-amplitude conversion

logic employs a COSINE function.

CFR1<12> = 1. The angle-to-amplitude conversion logic

employs a SINE function.

CFR1<11>: Not Used

CFR1<10>: Clear Phase Accumulator

CFR1<10> = 0 (default). The phase accumulator functions as

normal.

CFR1<10> = 1. The phase accumulator memory elements are

cleared and held clear until this bit is cleared.

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