DS1075

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PIN DESCRIPTIONS

Input/Output Pin (IN/OUT): This pin is the main oscillator output, with a frequency determined by clock

reference, M and N dividers. Except in programming mode this pin is always an output and will be

referred to as “OUT”. In programming mode this pin will be referred to as “IN”.

External Oscillator Input (OSCIN): This pin can be used to supply an external reference frequency to

the device.

Crystal Oscillator Connection (XTAL): A crystal can be connected between this pin and OSCIN to

provide an alternative frequency reference. If a crystal is not used this pin should be left open.

Output Enable Function (OE pin): The DS1075 also features a “synchronous” output enable. When

OE is at a high logic level the oscillator free runs. When this pin is taken low OUT is held low,

immediately if OUT is already low, or at it’s next high-to-low transition if OUT is high. This prevents

any possible truncation of the output pulse width when the enable is used. While the output is disabled

counters (/N) are reset. This results in a constant phase relationship between OE’s return to a high level

and the resulting OUT signal. When the enable is released OUT will make its first transition within one

to two clock periods of the master clock.

If the Power-Down function is selected (PDN bit = 1) a low logic level on this pin can be used to make

the device stop oscillating (active low) and go into a reduced power consumption state. The “Enabling

Sequencer” circuitry will first disable OUT in the same way as when OE is used. Next OUT0 will be

disabled in a similar fashion. Finally the oscillator circuitry will be disabled. In this mode both outputs

will go into a high impedance state. The power consumption in the power-down state is much less than if

OE is used because the internal oscillator (if used) is completely powered down. Even if an external

reference or a crystal is used all of the on-chip buffers are powered down to minimize current drain.

Consequently the device will take considerably longer to recover (i.e., achieve stable oscillation) from a

power-down condition than if the OE is used.

If the Select function is chosen (PDN bit = 0) this pin can be used to switch between the internal

external reference (or crystal oscillator).

Reference Output (OUT0 pin): A reference output, OUT0, is also available from the output of the

reference select mux. This output is especially useful as a buffered output of a crystal defined master

frequency. OUT0 is unaffected by the OE pin, but is disabled in a glitchless fashion if the device is

and there will be a corresponding reduction in overall power consumption.

USER-PROGRAMMABLE REGISTERS

The following registers can be programmed by the user to determine operating frequency and mode of

operation. Details of how these registers are programmed can be found in a later section, in this section