User Manual

19
4234F–SCR–10/05
AT83C24
Power Monitoring The AT83C24 needs only one power supply to run: VCC.
If the microcontroller outputs signals with a different electrical level, the host positive supply is
connected to EVCC.
EVCC and VCC pins can be connected together if they have the same voltage.
• If EVCC and VCC have different electrical levels:
The EVCC pin and RESET pin should be connected with a resist or bridge. RESET pin high
level must be higher than VIH (see Table 19). When EVCC drops, RESET pin level drops
too. A deactivation sequence starts if a card was active.
Then the AT83C24 resets if RESET pin stays low.
• If EVCC and VCC have the same value, then they should be connected:
The AT83C24 in tegrates an inter nal 3V regu lator to fee d its logic fr om the VC C supply. Th e
bit powermon allows the user to select if the inter nal PFD monitors VCC or the interna l regu-
lated 3V. If the PFD monitors VCC (POWERMON bit=0), a deactivation is perfor m ed if VCC
falls below VPFDP (see VPFDP value in the datasheet). Same deactivation is p erformed if
the internal 3V falls below VPFDP and POWERMON bit = 1.