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Semiconductor Group
31
System Reset
6
System Reset
6.1
Hardware Reset and Power-Up Reset
6.1.1
Reset Function and Circuitries
The hardware reset function incorporated in the SAB 80(C)515 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 7.6) is to be terminated.
In addition to the hardware reset, which is applied externally to the SAB 80(C)515, there is also the
possibility of an internal hardware reset. This internal reset will be initiated by the watchdog timer
(section 7.7).
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
V
CC
to allow a power-up reset with an external capacitor
only. An automatic reset can be obtained when
V
CC
is applied by connecting the reset pin to
V
SS
via
a capacitor as shown in figure 6-1 a) and c). After
V
CC
has been turned on the capacitor must hold
the voltage level at the reset pin for a specified time below the upper threshold of the Schmitt trigger
to effect a complete reset.
The time required is the oscillator start-up time plus 2 machine cycles, which, under normal
conditions, must be at least 10 - 20 ms for a crystal oscillator. This requirement is usually met using
a capacitor of 4.7 to 10 microfarad. The same considerations apply if the reset signal is generated
externally (figure 6-1 b) ). In each case it must be assured that the oscillator has started up properly
and that at least two machine cycles have passed before the reset signal goes inactive.
*
Содержание SAB 80515 Series
Страница 9: ...Semiconductor Group 9 Introduction Figure 1 2 Block Diagram ...
Страница 12: ...Semiconductor Group 12 Fundamental Structure Figure 2 1 Detailed Block Diagram ...
Страница 18: ...Semiconductor Group 18 Central Processing Unit Figure 3 1 Fetch Execute Sequence ...
Страница 22: ...Semiconductor Group 22 Memory Organization Figure 4 3 Mapping of the Lower Portion of the Internal Data Memory ...
Страница 30: ...Semiconductor Group 30 External Bus Interface Figure 5 1 a and b External Program Memory Execution ...
Страница 38: ...Semiconductor Group 38 On Chip Peripheral Components Figure 7 3 Output Driver Circuits of Ports 1 through 5 ...
Страница 59: ...Semiconductor Group 59 On Chip Peripheral Components Figure 7 16 a Functional Diagram Serial Interface Mode 0 ...
Страница 60: ...Semiconductor Group 60 On Chip Peripheral Components Figure 7 16 b Timing Diagram Serial Interface Mode 0 ...
Страница 61: ...Semiconductor Group 61 On Chip Peripheral Components Figure 7 17 a Functional Diagram Serial Interface Mode 1 ...
Страница 62: ...Semiconductor Group 62 On Chip Peripheral Components Figure 7 17 b Timing Diagram Serial Interface Mode 1 ...
Страница 73: ...Semiconductor Group 73 On Chip Peripheral Components Figure 7 25 A D Converter Block Diagram ...
Страница 83: ...Semiconductor Group 83 On Chip Peripheral Components Figure 7 33 a Timer 2 Block Diagram ...
Страница 111: ...Semiconductor Group 111 On Chip Peripheral Components Figure 7 54 Timing Diagram System Clock Output ...
Страница 113: ...Semiconductor Group 113 Interrupt System Figure 8 1 a Interrupt Structure of the SAB 80 C 515 80 C 535 ...
Страница 114: ...Semiconductor Group 114 Interrupt System Figure 8 1 b Interrupt Structure of the SAB 80 C 515 80 C 535 cont d ...
Страница 204: ...Semiconductor Group 204 Instruction Set XCH A Ri Operation XCH A Ri Bytes 1 Cycles 1 Encoding 1 1 0 0 0 1 1 i ...
Страница 215: ...Device Specifications Semiconductor Group 215 ...
Страница 217: ...Device Specifications Semiconductor Group 217 Pin Configuration P LCC 68 ...
Страница 219: ...Device Specifications Semiconductor Group 219 Logic Symbol ...
Страница 226: ...Device Specifications Semiconductor Group 226 Figure 1 Block Diagram ...
Страница 229: ...Device Specifications Semiconductor Group 229 Figure 2 Memory Address Spaces ...
Страница 239: ...Device Specifications Semiconductor Group 239 Figure 4 Block Diagram of the A D Converter ...
Страница 241: ...Device Specifications Semiconductor Group 241 Figure 5 Interrupt Request Sources ...
Страница 242: ...Device Specifications Semiconductor Group 242 Figure 6 Interrupt Priority Level Structure ...
Страница 268: ...Device Specifications Semiconductor Group 268 AC Testing Input Output Waveforms AC Testing Float Waveforms ...