C868 Datasheet, PDF (20/82 Pages) Infineon Technologies AG – 8-Bit Single-Chip Microcontroller

C868
Reset and Brownout
The reset input is an active low input. An internal Schmitt trigger is used at the input for
noise rejection. The RESET pin must be held low for at least tbd usec. But the CPU will
only exit from reset condition after the PLL lock had been detected.
During RESET at transition from low to high, C868 will go into normal mode if ALE/BSL
is high and bootstrap loading mode if ALE/BSL is low. A pullup to V_DDP or pulldown to
ground is recommended for pin ALE/BSL. TXD should have a pullup to V_DDP and should
not be stimulated externally during reset, as a logic low at this pin will cause the chip to
go into test mode if ALE/BSL is low.
Figure 10 shows the possible reset circuits, note that the RESET pin does not have an
internal pullup resistance.
V_DDP
a)
C868 BA
RESET
b)
C868 BA
&
RESET
V_DDP
c)
C868 BA
RESET
Figure 10 Reset Circuitries
An on-chip analog circuit detects brownout, if the core voltage V_DDC dips below the
threshold voltage V_THRESHOLD momentarily while RESET pin is high. If this detection is
active for tbd usec then the device will reset. When V_DDC recovers by exceeding
V_THRESHOLD while RESET is high, the reset is released once PLL is locked for 4096
clocks. Bit BO in the PMCON0 register is set when brownout detected if brownout
detection was enabled, this bit is cleared by hardware reset RESET and software. All
ports are tristated during brownout.
The V_THRESHOLD has a nominal value of 1.47V, a minimum value of 1.1V and a
maximum value of 1.8V.
Data Sheet
20
V 1.0, 2003-05