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PIC12F683 Datasheet(PDF) 91 Page - Microchip Technology |
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PIC12F683 Datasheet(HTML) 91 Page - Microchip Technology |
91 / 148 page 2004 Microchip Technology Inc. Preliminary DS41211B-page 89 PIC12F683 12.6 Watchdog Timer (WDT) For PIC12F683, the WDT has been modified from previous PIC12F683 devices. The new WDT is code and functionally compatible with previous PIC12F683 WDT modules and adds a 16-bit prescaler to the WDT. This allows the user to have a scaler value for the WDT and TMR0 at the same time. In addition, the WDT time-out value can be extended to 268 seconds. WDT is cleared under certain conditions described in Table 12-7. 12.6.1 WDT OSCILLATOR The WDT derives its time base from the 31 kHz LFINTOSC. The LTS bit does not reflect that the LFINTOSC is enabled. The value of WDTCON is ‘---0 1000’ on all Resets. This gives a nominal time base of 16 ms, which is com- patible with the time base generated with previous PIC12F683 microcontroller versions. A new prescaler has been added to the path between the INTRC and the multiplexers used to select the path for the WDT. This prescaler is 16 bits and can be programmed to divide the INTRC by 128 to 65536, giv- ing the time base used for the WDT a nominal range of 1 ms to 268s. 12.6.2 WDT CONTROL The WDTE bit is located in the Configuration Word register. When set, the WDT runs continuously. When the WDTE bit in the Configuration Word register is set, the SWDTEN bit (WDTCON<0>) has no effect. If WDTE is clear, then the SWDTEN bit can be used to enable and disable the WDT. Setting the bit will enable it and clearing the bit will disable it. The PSA and PS<2:0> bits (OPTION_REG) have the same function as in previous versions of the PIC12F683 family of microcontrollers. See Section 5.0 “Timer0 Module” for more information. FIGURE 12-9: WATCHDOG TIMER BLOCK DIAGRAM TABLE 12-7: WDT STATUS Note: When the Oscillator Start-up Timer (OST) is invoked, the WDT is held in Reset, because the WDT Ripple Counter is used by the OST to perform the oscillator delay count. When the OST count has expired, the WDT will begin counting (if enabled). Conditions WDT WDTE = 0 Cleared CLRWDT Command Oscillator Fail Detected Exit Sleep + System Clock = T1OSC, EXTRC, INTRC, EXTCLK Exit Sleep + System Clock = XT, HS, LP Cleared until the end of OST 31 kHz PSA 16-bit WDT Prescaler From TMR0 Clock Source Prescaler(1) 8 PS<2:0> PSA WDT Time-out To TMR0 WDTPS<3:0> WDTE from Configuration Word register 1 1 0 0 SWDTEN from WDTCON LFINTOSC Clock Note 1: This is the shared Timer0/WDT prescaler. See Section 5.4 “Prescaler” for more information. |
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