SAH-C515 SIEMENS [Siemens Semiconductor Group], SAH-C515 Datasheet - Page 37

• Manufacturer Part Number: SAH-C515
• Description: 8-Bit CMOS Microcontroller
• Manufacturer: SIEMENS [Siemens Semiconductor Group]

5
5.1
The hardware reset function incorporated in the C515 allows for an easy automatic start-up at a
minimum of additional hardware and forces the controller to a predefined default state. The
hardware reset function can also be used during normal operation in order to restart the device. This
is particularly done when the power-down mode is to be terminated.
Additional to the hardware reset, which is applied externally to the C515, there exists another
internal reset source, the watchdog timer. This chapter deals only with the external hardware reset.
The reset input is an active low input. An internal Schmitt trigger is used at the input for noise
rejection. Since the reset is synchronized internally, the RESET pin must be held low for at least two
machine cycles (24 oscillator periods) while the oscillator is running. With the oscillator running the
internal reset is executed during the second machine cycle and is repeated every cycle until RESET
goes high again.
During reset, pins ALE and PSEN are configured as inputs and should not be stimulated or driven
externally. (An external stimulation at these lines during reset activates several test modes which
are reserved for test purposes. This in turn may cause unpredictable output operations at several
port pins).
At the reset pin, a pullup resistor is internally connected to
external capacitor only. An automatic power-up reset can be obtained when
connecting the reset pin to
the voltage level at the reset pin for a specific time to effect a complete reset.
Semiconductor Group
Reset and System Clock Operation
Hardware Reset Operation
V
SS
via a capacitor. After
5-1
V
CC
has been turned on, the capacitor must hold
V
CC
to allow a power-up reset with an
Reset / System Clock
V
CC
is applied by
C515