XC864 Datasheet, PDF (59/118 Pages) Infineon Technologies AG – 8-Bit Single-Chip Microcontroller

XC864
Functional Description
3.7
Reset Control
The XC864 has five types of reset: power-on reset, hardware reset, watchdog timer
reset, power-down wake-up reset, and brownout reset.
When the XC864 is first powered up, the status of certain pins (see Table 21) must be
defined to ensure proper start operation of the device. At the end of a reset sequence,
the sampled values are latched to select the desired boot option, which cannot be
modified until the next power-on reset or hardware reset. This guarantees stable
conditions during the normal operation of the device.
In order to power up the system properly, the external reset pin RESET must be asserted
until V_DDC reaches 0.9*V_DDC. The delay of external reset can be realized by an external
capacitor at RESET pin. This capacitor value must be selected so that V_RESET reaches
0.4 V, but not before V_DDC reaches 0.9* V_DDC.
A typical application example is shown in Figure 20. V_DDP capacitor value is 300 nF.
V_DDC capacitor value is 220 nF. The capacitor connected to RESET pin is 100 nF.
Typically, the time taken for V_DDC to reach 0.9*V_DDC is less than 50 µs once V_DDP
reaches 2.3V. Hence, based on the condition that 10% to 90% V_DDP (slew rate) is less
than 500 µs, the RESET pin should be held low for 500 µs typically. See Figure 21.
5V
e.g. 300nF
220nF
typ.
100nF
VSSP VDDP ^VDDC
RESET
VSSC
EVR
30k
XC864
Figure 20 Reset Circuitry
Data Sheet
55
V 1.1, 2009-03