SAB80C517-M16 SIEMENS [Siemens Semiconductor Group], SAB80C517-M16 Datasheet - Page 24

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

Memory Organization
Stack Pointer, SFR Address 081 H
The stack pointer (SP) register is 8 bits wide. lt is incremented before data is stored during PUSH
and CALL executions and decremented after data is popped during a POP and RET (RETI)
execution, i.e. it always points to the last valid stack byte. While the stack may reside anywhere in
on-chip RAM, the stack pointer is initialized to 07 H after a reset. This causes the stack to begin at
location 08 H above register bank zero. The SP can be read or written under software control.
Datapointer, SFR Address 082 H and 083 H Datapointer Select Register, SFR Address 092 H
As a functional enhancement to standard 8051 controllers, the SAB 80C517 contains eight 16-bit
registers which can be used as datapointers. To be compatible with 8051 architecture, the
instruction set uses just one of these datapointers at a time. The selection of the actual datapointer
is done in special function register DPSEL (datapointer select register, address 92 H ).
Each 16-bit datapointer (DPTRx) register is a concatenation of registers DPHx (data pointer’s high
order byte) and DPLx (data pointer’s low order byte). These pointers are used in register-indirect
addressing to move program memory constants and external data memory variables, as well as to
branch within the 64-Kbyte program memory address space.
Since the datapointers are mainly used to access the external world, they are described in more
detail in section 5.2.
Ports 0 to 8
P0 to P8 are the SFR latches to port 0 to 8, respectively. The port SFRs 0 to 5 are bit-addressable.
Ports 0 to 6 are 8-bit I/O ports (that is in total 56 I/O lines) which may be used as general purpose
ports and which provide alternate output functions dedicated to the on-chip peripherals of the SAB
80C517.
Port 7 (8-bit) and port 8 (4-bit) are general purpose input ports and have no internal latch. That
means, these port lines are used for the 12 multiplexed input lines of the A/D converter but can also
be used as digital inputs. P7/P8 are the associated SFRs when the digital value is to be read by the
CPU. Both ports can be read only. You can find more about the ports in section 7.1 (parallel I/O).
Semiconductor Group
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