User`s manual

Changing the Signal Phase
This section explains how the phase of a sine wave generated by the DDS
(
[SOURce:]FREQuency[1]) subsystem is changed by writing phase data to
the Phase Modulation Registers.
The Phase Control
Registers
The following phase control registers are used to change the phase of the
sine wave generated by the DDS subsystem:
• Phase Modulation Registers:
base_addr + B3
16
through base_addr + B1
16
• Phase Load Strobe Register:
base_addr + 8B
16
The Phase Modulation
Registers
Phase Modulation Registers B3 and B1 contain the 12-bit phase modulation
data that is added to the output of the phase accumulator.
Address 15–8 76543210
base + B3
16
through
base + B1
16
unused Phase modulation value
Register B3: This register contains the eight most significant bits of the
12-bit phase modulation value (bits 11–4).
Register B1: Bits 7–4 of this register are the four least significant bits of the
12-bit phase modulation value (bits 3–0). Bits 3–0 of register B1 are
ignored.
The Phase Load
Strobe Register
Writing any value to the Phase Load Strobe Register adds the data in the
Phase Modulation Registers to the output of the phase accumulator.
Address 15–8 76543210
base + 8B
16
unused Strobe Data
Stobe Data: Writing any value to this register adds the data in the Phase
Modulation Registers to the output of the phase accumulator. Once the
phase has been added, it takes 14 reference oscillator clock cycles for the
new phase to appear at the output.
Appendix C Register-Based Programming 495