Datasheet

PIC24FJ16MC101/102 AND PIC24FJ32MC101/102/104
DS39997C-page 66 Preliminary © 2011-2012 Microchip Technology Inc.
FIGURE 6-2: SYSTEM RESET TIMING
Reset
Run
Device Status
V
DD
VPOR
Vbor
VBOR
POR
BOR
SYSRST
TPWRT
TPOR
TBOR
Oscillator Clock
T
OSCD TOST
TLOCK
Time
FSCM
T
FSCM
1
2
3
4
5
6
1. POR: A POR circuit holds the device in Reset when the power supply is turned on. The POR circuit is active until V
DD crosses the
V
POR threshold and the delay TPOR has elapsed.
2. BOR: The on-chip voltage regulator has a BOR circuit that keeps the device in Reset until V
DD crosses the VBOR threshold and the
delay T
BOR has elapsed. The delay TBOR ensures the voltage regulator output becomes stable.
3. PWRT Timer: The power-up timer continues to hold the processor in Reset for a specific period of time (T
PWRT) after a BOR. The
delay T
PWRT ensures that the system power supplies have stabilized at the appropriate level for full-speed operation. After the delay
T
PWRT has elapsed, the SYSRST becomes inactive, which in turn enables the selected oscillator to start generating clock cycles.
4. Oscillator Delay: The total delay for the clock to be ready for various clock source selections are given in Tab le 6-1. Refer to
Section 8.0 “Oscillator Configuration” for more information.
5. When the oscillator clock is ready, the processor begins execution from location 0x000000. The user application programs a GOTO
instruction at the Reset address, which redirects program execution to the appropriate start-up routine.
6. The Fail-Safe Clock Monitor (FSCM), if enabled, begins to monitor the system clock when the system clock is ready and the delay
T
FSCM elapsed.
TABLE 6-2: OSCILLATOR PARAMETERS
Symbol Parameter Value
VPOR POR threshold 1.8V nominal
T
POR POR extension time 30 μs maximum
VBOR BOR threshold 2.5V nominal
T
BOR BOR extension time 100 μs maximum
TPWRT Power-up time
delay
64 ms nominal
T
FSCM Fail-safe Clock
Monitor Delay
900 μs maximum
Note: When the device exits the Reset condi-
tion (begins normal operation), the
device operating parameters (voltage,
frequency, temperature, etc.) must be
within their operating ranges, otherwise
the device may not function correctly. The
user application must ensure that the
delay between the time power is first
applied, and the time SYSRST
becomes
inactive, is long enough to get all
operating parameters within
specification.