Datasheet

DS1085
5 of 21
REGISTER FUNCTIONS
The user-programmable registers can be used to determine the mode of operation (MUX), operating
frequency (DAC, OFFSET, DIV), and bus settings (ADDR). The functions of the registers are described
in this section, but details of how these registers are programmed can be found in a later section. The
register settings are nonvolatile, with the values being stored automatically or as required in EEPROM
when the registers are programmed through the SDA and SCL pins.
DAC WORD (Address 08h)
MSB LSB MSB LSB
d9 d8 d7 d6 d5 d4 d3 d2 d1 d0 X X X X X X
First Data Byte Second Data Byte
X = Don’t care.
The DAC word (d0–d9) controls the frequency of the master oscillator. The resolution of this register
depends on the step size of the device. The absolute frequency of the device also depends on the value of
the OFFSET register (see Table 5 and 6).
Table 5. DEFAULT DAC SETTINGS
DS1085Z-10
DS1085Z-25 DS1085Z-50
Frequency DAC Offset Frequency DAC Offset Frequency DAC Offset
97.1MHz 500 OS 104.6MHz 600 OS 101.8MHz 500 OS
For any given value of OFFSET the master oscillator frequency can be derived as follows:
Frequency = Min Frequency + DAC x Step Size
where: Min frequency is the lowest frequency shown in Table 6 for the corresponding offset.
DAC is the value of the DAC register (0–1023).
Step size is the step size of the device (10kHz, 25kHz, or 50kHz).
OS is the decimal, integer value of the five MSBs of the RANGE register.
OFFSET BYTE
(Address 0Eh)
MSB LSB
X X X O4 O3 O2 O1 O0
X = Don’t care.
The OFFSET byte (O0–O4) determines the range of frequencies that can be obtained within the absolute
minimum and maximum range of the oscillator. Correct operation of the device is not guaranteed for
values of OFFSET not shown in Table 6.