PIC18F to PIC24F Migration: An Overview - Microchip

DOZE MODESPIC24F devices feature an additional Doze mode optionto reduce power consumption while allowing the applicationto continue running. Doze mode permits the CPU torun at a reduced clock rate while the peripherals areclocked at full speed. It is enabled by setting the DOZENbit (CLKDIV). The CPU peripheral clock ratio isselected using the DOZE bits (CLKDIV), with arange of 1:128 (slowest) to 1:1 (full speed). An option todisable Doze mode on an interrupt is available throughthe Recover on Interrupt bit, ROI (CLKDIV).PIC18F devices have no equivalent feature.PERIPHERAL MODULE DISABLEIn PIC24F devices, the PMD feature reduces peripheralcurrent consumption to the absolute minimum possible.Peripherals which support PMD have an associatedcontrol bit in one of the PMD registers. When enabled,all clock sources are disconnected from the peripheral,and all SFR registers associated with it appear as unimplementedmemory. This is a contrast to the SelectivePeripheral Idle, where the module is partially powereddown but remains accessible.There is no equivalent feature in PIC18F architecture.ADDITIONAL PIC24F FEATURESThe internal voltage regulator can be brought into alow-power mode by setting the VREGS bit(RCON). In this mode, the voltage regulatorsupplies only enough power to maintain RAM states. Ifany peripherals are active, this mode cannot be used.MIGRATING A TYPICAL SETUPFor straight migrations of a PIC18F application usingPower-Saving modes, there is a tight correspondencebetween PIC18F and PIC24F instructions. Users willneed to change references from SCS1:SCS0 to theequivalent mode using NOSC2:NOSC0 (plus the additionof the register unlocking sequence). Additionally,all SLEEP instructions will need to be changed to theappropriate PWRSV n equivalent, and references toIDLEN removed.MIGRATION CONSIDERATIONS• The voltage/frequency characteristics of thePIC18F and PIC24F architectures are significantlydifferent and will affect clock switching decisions.The PIC24F voltage supply range (2.0V to3.6V) is narrower than for PIC18F devices, suchas the PIC18F8722. Applications that changeclock frequencies, due to reduced power supplyvoltage, may not need to switch at all, since thePIC24F can operate at higher speeds across awider range of voltage. Also note that PIC18FXXJFlash devices, such as the PIC18F87J10, haveV/F characteristics that are similar to the PIC24Ffamily.• The lower maximum VDD of PIC24F devices mayalso impact the design of an application migratedfrom PIC18F devices. Refer to the appropriateproduct data sheets for more information onoperating voltage range and Power-Managedmodes.DS39764A-page 24© 2006 Microchip Technology Inc.