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70592C 数据表(PDF) 72 Page - Microchip Technology |
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70592C 数据表(HTML) 72 Page - Microchip Technology |
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72 / 314 page  PIC24HJXXXGPX06A/X08A/X10A DS70592C-page 72 © 2011 Microchip Technology Inc. TABLE 6-3: RESET DELAY TIMES FOR VARIOUS DEVICE RESETS 6.2.1 POR AND LONG OSCILLATOR START-UP TIMES The oscillator start-up circuitry and its associated delay timers are not linked to the device Reset delays that occur at power-up. Some crystal circuits (especially low-frequency crystals) have a relatively long start-up time. Therefore, one or more of the following conditions is possible after the Reset signal is released: • The oscillator circuit has not begun to oscillate • The Oscillator Start-up Timer has not expired (if a crystal oscillator is used) • The PLL has not achieved a lock (if PLL is used) The device will not begin to execute code until a valid clock source has been released to the system. There- fore, the oscillator and PLL start-up delays must be considered when the Reset delay time must be known. 6.2.2 FAIL-SAFE CLOCK MONITOR (FSCM) AND DEVICE RESETS If the FSCM is enabled, it begins to monitor the system clock source when the Reset signal is released. If a valid clock source is not available at this time, the device automatically switches to the FRC oscillator and the user can switch to the desired crystal oscillator in the Trap Service Routine. 6.2.2.1 FSCM Delay for Crystal and PLL Clock Sources When the system clock source is provided by a crystal oscillator and/or the PLL, a small delay, TFSCM, is auto- matically inserted after the POR and PWRT delay times. The FSCM does not begin to monitor the system clock source until this delay expires. The FSCM delay time is nominally 500 μs and provides additional time for the oscillator and/or PLL to stabilize. In most cases, the FSCM delay prevents an oscillator failure trap at a device Reset when the PWRT is disabled. 6.3 Special Function Register Reset States Most of the Special Function Registers (SFRs) associ- ated with the CPU and peripherals are reset to a particular value at a device Reset. The SFRs are grouped by their peripheral or CPU function and their Reset values are specified in each section of this manual. The Reset value for each SFR does not depend on the type of Reset, with the exception of two registers. The Reset value for the Reset Control register, RCON, depends on the type of device Reset. The Reset value for the Oscillator Control register, OSCCON, depends on the type of Reset and the programmed values of the oscillator Configuration bits in the FOSC Configuration register. Reset Type Clock Source SYSRST Delay System Clock Delay FSCM Delay See Notes POR EC, FRC, LPRC TPOR + TSTARTUP + TRST —— 1, 2, 3 ECPLL, FRCPLL TPOR + TSTARTUP + TRST TLOCK TFSCM 1, 2, 3, 5, 6 XT, HS, SOSC TPOR + TSTARTUP + TRST TOST TFSCM 1, 2, 3, 4, 6 XTPLL, HSPLL TPOR + TSTARTUP + TRST TOST + TLOCK TFSCM 1, 2, 3, 4, 5, 6 MCLR Any Clock TRST —— 3 WDT Any Clock TRST —— 3 Software Any clock TRST —— 3 Illegal Opcode Any Clock TRST —— 3 Uninitialized W Any Clock TRST —— 3 Trap Conflict Any Clock TRST —— 3 Note 1: TPOR = Power-on Reset delay (10 μs nominal). 2: TSTARTUP = Conditional POR delay of 20 μs nominal (if on-chip regulator is enabled) or 64 ms nominal Power-up Timer delay (if regulator is disabled). TSTARTUP is also applied to all returns from powered-down states, including waking from Sleep mode, only if the regulator is enabled. 3: TRST = Internal state Reset time (20 μs nominal). 4: TOST = Oscillator Start-up Timer. A 10-bit counter counts 1024 oscillator periods before releasing the oscillator clock to the system. 5: TLOCK = PLL lock time (20 μs nominal). 6: TFSCM = Fail-Safe Clock Monitor delay (100 μs nominal). |
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