User`s manual

The Frequency Load
Strobe Register
Writing any value to the Frequency Load Strobe Register loads the contents
of the Phase Increment Registers into the DDS micro-chip.
Address 158 76543210
base + 8D
16
unused Strobe Data
Stobe Data: Writing any value to this register loads the contents of the
Phase Increment Registers into the DDS micro-chip. Once the data has
been loaded, it takes 20 reference oscillator clock cycles for the new
frequency to appear at the output.
The Sample/Hold and
ROSC/N Control
Register
The Sample/Hold and ROSC/N Control Register enables and disables signal
sampling, and specifies the N value used to generate ROSC/N frequencies.
Address 158 76543210
base + 63
16
unused SHOLD SMUX2 SMUX1 SMUX0
SHOLD: Setting bit 7 to a ’1’ causes sample signals to be ignored. This bit
is set while setting the divide-by-n counter.
SMUX2–SMUX0: bits 2–0 select N as follows:
0 0 0 = selects ROSC/1
0 0 1 = selects ROSC/2
0 1 0 = selects ROSC/3
0 1 1 = selects ROSC/2N
The ROSC/N Divider
Registers
The ROSC/N Divider Registers contain the value of (N-1) when 2N is
greater than or equal to 4. The reference oscillator (ROSC) will be divided
by 4 through 131,072 when the registers are loaded with 1 through 65,535.
Address 158 76543210
base + 7D
16
through
base + 7F
16
unused value
Register 7D: Contains the most significant byte of the value of (N-1).
Register 7F: Contains the least significant byte of the value of (N-1).
488 Register-Based Programming Appendix C