Rainbow Electronics AT83C24NDS - Manual (Page 19)

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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 resistor 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 integrates an internal 3V regulator to feed its logic from the VCC supply. The
bit powermon allows the user to select if the internal PFD monitors VCC or the internal regu-
lated 3V. If the PFD monitors VCC (POWERMON bit=0), a deactivation is performed if VCC
falls below VPFDP (see VPFDP value in the datasheet). Same deactivation is performed if
the internal 3V falls below VPFDP and POWERMON bit = 1.