SAB80C517-M16 SIEMENS [Siemens Semiconductor Group], SAB80C517-M16 Datasheet - Page 35

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

System 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.
Figure 6-1
Reset Circuitries
A correct reset leaves the processor in a defined state. The program execution starts at location
0000 H . The default values of the special function registers (SFR) to which they are forced during
reset are listed in table 6-1. After reset is internally accomplished the port latches of ports 0 to 6
default in 0FF H . This leaves port 0 floating, since it is an open drain port when not used as data/
address bus. All other I/O port lines (ports 1 through 6) output a one (1). Ports 7 and 8, which are
input-only ports, have no internal latch and therefore the contents of the special function registers
P7 and P8 depend on the levels applied to ports 7 and 8.
The contents of the internal RAM of the SAB 80C517 is not affected by a reset. After power-up the
contents is undefined, while it remains unchanged during a reset it the power supply is not turned
off.
Semiconductor Group
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