Datasheet

153
4337K–USB–04/08
AT89C5130A/31A-M
23. Power Monitor
The POR/PFD function monitors the internal power-supply of the CPU core memories and the
peripherals, and if needed, suspends their activity when the internal power supply falls below a
safety threshold. This is achieved by applying an internal reset to them.
By generating the Reset the Power Monitor insures a correct start up when AT89C5131 is pow-
ered up.
23.1 Description
In order to startup and maintain the microcontroller in correct operating mode, V
CC
has to be sta-
bilized in the V
CC
operating range and the oscillator has to be stabilized with a nominal amplitude
compatible with logic level VIH/VIL.
These parameters are controlled during the three phases: power-up, normal operation and
power going down. See Figure 23-1.
Figure 23-1. Power Monitor Block Diagram
Note: 1. Once XTAL1 High and low levels reach above and below VIH/VIL. a 1024 clock period delay
will extend the reset coming from the Power Fail Detect. If the power falls below the Power Fail
Detect threshold level, the Reset will be applied immediately.
The Voltage regulator generates a regulated internal supply for the CPU core the memories and
the peripherals. Spikes on the external Vcc are smoothed by the voltage regulator.
The Power fail detect monitor the supply generated by the voltage regulator and generate a
reset if this supply falls below a safety threshold as illustrated in the Figure 23-2 below.
VCC
Power On Reset
Power Fail Detect
Voltage Regulator
XTAL1
(1)
CPU core
Memories
Peripherals
Regulated
Supply
RST pin
Hardware
Watchdog
PCA
Watchdog
Internal Reset