Datasheet

© 2007-2011 Microchip Technology Inc. DS70265E-page 67
dsPIC33FJ12MC201/202
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 programmable 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 oper-
ation. After the delay T
PWRT has elapsed, the SYSRST becomes inactive, which in turn enables the selected oscillator to start gen-
erating clock cycles.
4. Oscillator Delay: The total delay for the clock to be ready for various clock source selections are given in Tabl e 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
V
POR POR threshold 1.8V nominal
T
POR POR extension time 30 μs maximum
V
BOR BOR threshold 2.5V nominal
T
BOR BOR extension time 100 μs maximum
T
PWRT Programmable
power-up time delay
0-128 ms nominal
TFSCM 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, other-
wise the device may not function cor-
rectly. 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.