SAB80515 Datasheet, PDF (32/270 Pages) Siemens Semiconductor Group – 8-Bit Single-Chip Microcontroller Family

System Reset
Figure 6-1 a) - c)
Reset Circuitries
A correct reset leaves the processor in a defined state. The program execution starts at location
0000H. The default values of the special function registers (SFR) during and after reset are listed
in table 6-1. After reset is internally accomplished the contents of the port latches of port 0 to 5 is
0FFH. 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 5) output a one (1).
In the MYMOS versions, the analog input lines AN0 to AN7 can only be used as inputs.
In the ACMOS versions these lines may also be used as digital inputs. In this case they are
addressed as an additional input port (port 6) via special function register P6 (0DBH) Since port 6
has no internal latch, the contents of SFR P6 only depends on the levels applied to the input lines.
For details about this port please refer to section 7.1 (Parallel I/O).
The contents of the internal RAM of the SAB 80(C)515 is not affected by a reset. After power-up the
contents is undefined, while it remains unchanged during a reset if the power supply is not turned
off.
Semiconductor Group
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