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SH3001 Datasheet(PDF) 7 Page - Semtech Corporation |
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SH3001 Datasheet(HTML) 7 Page - Semtech Corporation |
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7 / 20 page  SH3001 MicroBuddy™ SYSTEM MANAGEMENT Copyright ©2002-2005 Semtech Corporation 7 V1.15 www.semtech.com Special Operating Modes The SH3001 can operate stand-alone, without connections to the In and Out terminals of the host’s oscillator. For example, a bank of SH3001 chips can generate several different frequencies for simultaneous use in the system, all controlled by a single micro (and possibly sharing one 32.768 kHz crystal by chaining the CLK32 pin to XIN pin on the next device). In this case the CLKIN pin should be connected to VSS. The clock output on the CLKOUT pin is continuous; the correct operating mode is automatically recognized by the SH3001. Real-Time Support The SH3001 has two support modules that are specifically designed for various real time support functions. They are the Real-Time Clock and the Periodic Interrupt / Wakeup Timer. Both of these units as well as other functions of the SH3001 depend on the internal 32.768 kHz clock for accuracy. With one external component (a 32.768 kHz crystal), the SH3001 can provide a processor clock accuracy of ± 256 ppm (± 0.0256%) and the accuracy of the real- time system of ± 4 ppm (± 0.0004%). A microcontroller might not have a STOP command. With the SH3001, this controller can do a “simulated” STOP by issuing an instruction to the SH3001 to stop the clock. This command is accepted only if the Periodic Interrupt / Wakeup Timer has started (otherwise, once the system is put to sleep, it would never wake up again). This mode of operations is only possible if the host processor is capable of correct operations with clock frequency down to zero, and keeps all of the internal RAM alive while the clock is stopped. Low Frequency (LF) Oscillator System This module provides the 32.768 kHz clock to all internal circuits and to the dedicated output pin, CLK32. If enabled, the CLK32 output continues normal operations when VDD is absent and backup power is available. When the power is first applied to the SH3001, the RC oscillator takes over. It supplies the 32.768 kHz clock for start-up and initialization. Once the crystal has started and stabilized, the internal 32.768 kHz clock switches to the very accurate crystal frequency; see Figure 2. 5 6 7 VREG RC Oscillator 13 Internal 32.768 kHz Clock X-tal stable? Internal RREF 32.768 kHz Crystal 12.5 pF Load Capacitance Figure 2. Simplified LF Oscillator System 1 CLK32 XIN XOUT CLKSEL 8 VSS VSS CLK32 ON 4-bit Value 6-bit Value 4-bit Value Lock / Unlock Logic Lock Logic INTERNAL RREF ON From / To Serial I/O |
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