Intel SA-1100 manual MHz Oscillator Specifications B, System Specifications

3.6864–MHz Oscillator Specifications B

A 3.6864-MHz crystal oscillator is integrated on the Intel® StrongARM® SA-1100 Microprocessor (SA-1100) for use as a reference frequency for the PLLs that generate the internal clocks to the processor. The phase noise of this reference frequency should be minimized because it could be amplified by the PLLs, resulting in PLL output frequency jitter. For this application, the long-term stability and the temperature effect on the frequency are not important because they affect the frequency by less than 1%. The oscillator circuit is designed to work across a range of crystal parameters so that the system designer can choose from several 3.6864-MHz crystals available on the market. In normal operation, the pins of the crystal, Q1 and Q2, are connected to the SA-1100 pins, PXTAL and PEXTAL. Note that a 3.5795-MHz crystal can also be used, but in order to meet the frequency specifications of several of the integrated I/O ports, a 3.6864-MHz crystal is required.

In some applications, it may be desirable to provide the 3.6864-MHz reference from an external signal source. This option is supported by the SA-1100. See Chapter 8, “Clocks” .

B.1 Specifications

This section includes specifications for the oscillator circuit and the quartz crystal.

B.1.1 System Specifications

This section includes the specifications of the oscillator circuit. It assumes that the crystal used meets the specifications given in the following sections.

Temperature Range

This is the junction temperature range for the oscillator circuit on the SA-1100. The crystal itself may be at the ambient temperature; the oscillator circuit integrated on the SA-1100 is most likely operating at a higher temperature that is dependent on the activity of the SA-1100.

Current Consumption

Because this oscillator might run during the sleep mode of the processor, the power consumption is critical. The specified current consumption is for the oscillator only. The power associated with the oscillator output buffer is not included because this buffer is powered down in sleep.

Startup Time

This specification depends on the crystal characteristics and the layout of the printed circuit board (PCB). The value given assumes that the crystal and board layout conform to the values given in the remainder of this document. The critical parameters in the crystal specification are the shunt capacitance (Co) and the motional resistance (Rm), which must be no greater than the maximums specified. The critical parameters in the PCB layout are the parasitic capacitances between PXTAL and PEXTAL, and between either of these nodes and VSS. Note that in some applications, such as a system that includes a socketed SA-1100, it may be difficult to meet the parasitic capacitances specified. While the 3.6864-MHz oscillator will start with parasitic capacitances, which are

SA-1110 Developer’s Manual B-1