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DIFFERENT WAYS TO RESET ST7 MICROCONTROLLER

5 PROS AND CONS OF DIFFERENT TYPES OF RESET MECHANISM

This section includes the advantages and disadvantages of both External Reset and Internal

LVD. In the section below ‘+’ indicates advantages and ‘-’ indicates disadvantages.

5.1 EXTERNAL RESET CIRCUIT

+ It can be used for very slow rising supply. External RCD circuit is suitable for fairly fast VDD

slopes. Transistor based Reset circuits can be used for very slow VDD slopes

- Extra components required resulting in additional cost and extra space on PCB

- Current consumption (Transistor based External Reset circuits) higher than that of Internal

LVD

5.2 INTERNAL LVD

+ Each MCU has three programmable thresholds

+ No additional cost, as this feature come with the microcontroller

+ No extra components, no extra space on the PCB

- LVD current consumption quite high when compared to External LVD

- VDD slope range is limited

- Supply Voltage should rise monotonously for correct functionality of LVD

- Poor accuracy of reset voltage threshold

5.3 EXTERNAL LVD

+ Could be useful if the application requires a specific threshold (other than LVD threshold)

+ Power consumption much less (6uA for STM809-812)

+ Offers excellent immunity to supply transients

+ A stand alone Reset can monitor a special voltage for a peripheral

+ Several stand alone resets can be put in parallel.

+ Reset threshold more accurate

- One chip can provide only one threshold (Internal LVD has three programmable thresholds)

- Extra space on PCB

- Additional cost, cost: 1 to 10K units: $0.16