W79E804A/803A/802A
22. POWER MONITORING FUNCTION
Power-On Detect and Brownout are two additional power monitoring functions implemented in
W79E804 series to prevent incorrect operation during power up and power drop or loss.
22.1 Power On Detect
The Power–On Detect function is a designed to detect power up after power voltage reaches to a level
where Brownout Detect can work. After power on detect, the POR (PCON.4) will be set to “1” to
indicate an initial power up condition. The POR flag will be cleared by software.
22.2 Brownout Detect
The Brownout Detect function is detect power voltage is drops to brownout voltage level, and allows
preventing some process work or indicate power warming. The W79E804 series have two brownout
voltage levels to select by BOV (CONFIG1.4). If BOV =0 that brownout voltage level is 3.8V, If BOV =
1 that brownout voltage level is 2.5V. When the Brownout voltage is drop to select level, the brownout
detector will detect and keeps this active until VDD is returns to above brownout Detect voltage. The
Brownout Detect block is as follow.
Brownout
Detect
Circuit
0
BOF
1
BOI
To Reset
To Brownout interrupt
BOD
(Enable Brownout Detect)
Figure 22-1: Brownout Detect Block
When Brownout Detect is enabled by BOD (AUXR1.6), the BOF (PCON.5) flag will be set and
brownout reset will occur. If BOI (AUXR1.5) is set to “1”, the brownout detect will cause interrupt via
the EA (IE.7) and EBO (IE.5) bits is set. BOF is cleared by software.
In order to guarantee a correct detection of Brownout, The VDD fail time must be slower than
50mV/us, and rise time is slower than 2mV/us to ensure a proper reset.
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