app182| Application Note
Application Note 182
Frequency Calculator for the DS1085/DS1085L EconOscillator
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INTRODUCTION
The DS1085/DS1085L produces a wide range of frequencies (8.1kHz to 133MHz and 4.1kHz to 66MHz, respectively) on the main oscillator output (OUT1) and 8.2MHz to 133MHz and 4.13MHz to 66MHz, respectively, on the reference oscillator output (OUT0). The DS1085/DS1085L allows the user to divide down the frequency (as in the DS1077/DS1077L) but also change the master frequency using DAC and OFFSET. The frequency can be changed by using the internal registers. The DS1085 and DS1085L have the same internal registers, which will be discussed below. The default frequency, DAC step size, DAC default, and OFFSET step size are different between devices and device versions (see Table 1). To assist in determining which registers to change, an interactive frequency calculator for the DS1085/DS1085L has been developed. The general equations the frequency calculator uses are given in the DS1085/DS1085L Registers section, for more details and the specific equations see the Appendix.
DEVICE DEFAULTS Table 1
DS1085 Device Version -10 -25 -50 DS1085L Device Version -5 -12 -25 Frequency 97.1MHz 104.6MHz 101.8MHz Frequency 48.58MHz 52.3MHz 50.9MHz DAC Step Size 10kHz 25kHz 50kHz DAC Step Size 5kHz 12.5kHz 25kHz DAC Default 500 600 500 DAC Default 500 600 500 OFFSET Step Size 5.12MHz 6.4MHz 6.4MHz OFFSET Step Size 2.56MHz 3.2MHz 3.2MHz
DS1085/DS1085L REGISTERS
The DS1085/DS1085L's frequencies can be programmed by changing the four frequency variables. The four frequency variables are the prescaler M, divisor N, OFFSET, and DAC. Descriptions of each register and how the frequency is affected by each variable are described below. Refer to the block diagram in the datasheet for more information. Prescalers (MUX Register) (Address 02h) The prescalers divide down the output frequency. P0 is the OUT0 prescaler, and P1 is the OUT1 prescaler. The MUX register sets the prescalers (bits 1 to 4). See Tables 2 and 3 for more information.
PRESCALERS Table 2
0M1 0M0 (Bit 4) (Bit 3) 0 0 0 1 1 0 1 1 *Factory default setting Prescaler P0 Divisor "M" 1* 2 4 8 1M1 (Bit 2) 0 0 1 1
1 of 7
1M0 (Bit 1) 0 1 0 1
Prescaler P1 Divisor "M" 1* 2 4 8
03/06/02
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