SAB80C517-M16 SIEMENS [Siemens Semiconductor Group], SAB80C517-M16 Datasheet - Page 34

• Manufacturer Part Number: SAB80C517-M16
• Description: 8-Bit CMOS Single-Chip Microcontroller
• Manufacturer: SIEMENS [Siemens Semiconductor Group]

6
6.1
6.1.1
The hardware reset function incorporated in the SAB 80C517 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 (see section 7.7) is to be terminated.
Additionally to the hardware reset, which is applied externally to the SAB 80C517, there are two
internal reset sources, the watchdog timer and the oscillator watchdog. They are described in detail
in section 7.8 "Fail-Save Mechanisms". The chapter at hand only deals with the external hardware
reset.
The reset input is an active low input at pin 10 (RESET). 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 in which RESET
is low 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 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).
A pullup resistor is internally connected to
only. An automatic reset can be obtained when
a capacitor as shown in figure 6-1 a) and c). After
the voltage level at the reset pin for a specified time below the upper threshold of the Schmitt trigger
to effect a complete reset.
Semiconductor Group
System Reset
Hardware Reset and Power-Up Reset
Reset Function and Circuitries
V
CC
to allow a power-up reset with an external capacitor
V
35
CC
V
is applied by connecting the reset pin to
CC
has been turned on, the capacitor must hold
System Reset
V
SS
via