WDT có một postscaler có thể kéo dài thời gian Thiết lập lại WDT. Postscaler được chọn tại thời điểm lập trình thiết bị, bởi giá trị bằng văn bản cho đăng ký cấu hình CONFIG2H. Chế độ Power-down được nhập bằng cách thực hiện một lệnh giấc ngủ. Nếu kích hoạt, Timer Watchdog sẽ được xóa, nhưng tiếp tục chạy, bit PD (RCON) là xóa bit (RCON) TO được thiết lập, và | PIC18FXX2 WDT POSTSCALER The WDT has a postscaler that can extend the WDT Reset period. The postscaler is selected at the time of the device programming by the value written to the CONFIG2H configuration register. FIGURE 19-1 WATCHDOG TIMER BLOCK DIAGRAM WDT Time-out WDTPS2 WDTPS0 Note WDPS2 WDPS0 are bits in register CONFIG2H. TABLE 19-2 SUMMARY OF WATCHDOG TIMER REGISTERS Name Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0 CONFIG2H WDTPS2 WDTPS2 WDTPS0 WDTEN RCON IPEN RI TO PD POR BOR WDTCON SWDTEN Legend Shaded cells are not used by the Watchdog Timer. DS39564C-page 204 2006 Microchip Technology Inc. PIC18FXX2 Power-down Mode SLEEP Power-down mode is entered by executing a SLEEP instruction. If enabled the Watchdog Timer will be cleared but keeps running the PD bit RCON 3 is cleared the TO RCON 4 bit is set and the oscillator driver is turned off. The I O ports maintain the status they had before the SLEEP instruction was executed driving high low or hi-impedance . For lowest current consumption in this mode place all I O pins at either VDD or VSS ensure no external circuitry is drawing current from the I O pin power-down the A D and disable external clocks. Pull all I O pins that are hi-impedance inputs high or low externally to avoid switching currents caused by floating inputs. The T0CKI input should also be at Vdd or Vss for lowest current consumption. The contribution from on-chip pull-ups on PORTB should be considered. The MCLR pin must be at a logic high level Vihmc . WAKE-UP FROM SLEEP The device can wake-up from SLEEP through one of the following events 1. External RESET input on MCLR pin. 2. Watchdog Timer Wake-up if WDT was enabled . 3. Interrupt from INT pin RB port change or a Peripheral Interrupt. The following peripheral interrupts can wake the device from SLEEP 1. PSP read or write. 2. TMR1 interrupt. Timer1 must be operating as an asynchronous counter. 3. TMR3 interrupt. Timer3 must be operating as an asynchronous counter. 4.
