Rainbow Electronics AT89C5122 - Manual (Page 172)

172
AT8xC5122/23
4202E–SCR–06/06
Microcontroller Reset
Introduction The internal reset is used to start up (cold reset) or to re-start (warm reset) the micro-
controller activity. When the reset is applied (active state), all internal registers are
initialized so that the microcontroller starts from a known and clean state for the program
always runs as expected.
The reset is released (inactive state) when the following conditions are internally met :
– The power supply has reatched a minimum level which garantees that the
microcontroller works properly
– The on-chip oscillator has reached a minimum oscillation level which
ensures a good noise to signal ratio and a correct internal duty cycle
– the active state duration is at least two machine cycles.
If one of the above conditions is not met the microcontroller is not correctly reset and
might not work properly.
The internal reset comes from four different sources :
– Reset pin
– Power On Reset (POR)
– Power Fail Detector (PFD)
– Hardware Watch-Dog Timer (WDT)
Figure 101. Reset bock diagram
Watch Dog
RST
Internal Reset
Timer
Microcontroller
Vcc
3.3V Internal
Digital Regulator
C51
Core
VCore
POR
PFD