The internal reset is immediately asserted when a reset source goes active. The
internal reset is kept asserted until the reset source is released and the start-up
sequence is completed. The start-up sequence includes three steps, as follows.
- 1.The first step after the reset
source has been released consists of the device counting the reset start-up
time. The purpose of this reset start-up time is to ensure that supply voltage
has reached sufficient levels. The reset start-up time is counted using the
internal 128kHz oscillator.
Note: The actual supply voltage is not monitored by the start-up logic. The
device will count until the reset start-up time has elapsed even if the
device has reached sufficient supply voltage levels earlier.
- 2.The second step is to count the
oscillator start-up time, which ensures that the calibrated internal oscillator
has reached a stable state before it is used by the other parts of the system.
The calibrated internal oscillator needs to oscillate for a minimum number of
cycles before it can be considered stable.
- 3.The last step before releasing
the internal reset is to load the calibration and the configuration values from
the Non-Volatile Memory to configure the device properly. The configuration time
is listed in the next table.
There are two start-up time options which will be supported :
- Normal start-up time: 64ms
- Fast start-up time: 8ms
Table 1. Start-up Times when Using the
Internal Calibrated Oscillator with Normal start-up time
| Reset |
Oscillator |
Configuration |
Total start-up time |
| 64ms |
6cycles |
21cycles |
64ms + 6 oscillator cycles + 21 system clock cycles
(1) |
Table 2. Start-up Times when Using the Internal Calibrated Oscillator with shorter startup
time
| Reset |
Oscillator |
Configuration |
Total start-up time |
| 8ms |
6cycles |
21cycles |
8 ms + 6 oscillator cycles + 21 system clock cycles
(1) |
Note:
- 1.After powering up the device or
after a reset the system clock is automatically set to calibrated internal 8MHz
oscillator, divided by 8