SAB80C517A-N18 Siemens Semiconductor Group, SAB80C517A-N18 Datasheet - Page 20

• Manufacturer Part Number: SAB80C517A-N18
• Description: 8-Bit CMOS Single-Chip Microcontroller
• Manufacturer: Siemens Semiconductor Group

Data Memory ('Code Space')
The data memory space consists of an internal and an external memory space. The
SAB 80C517A contains another 2 Kbyte on On-Chip RAM above the 256-bytes internal RAM
of the base type SAB 80C517. This RAM is called XRAM in this document.
External Data Memory
Up to 64 Kbyte external data memory can be addressed by instructions that use 8-bit or 16-bit
indirect addressing. For 8-bit addressing MOVX instructions in combination with registers R0
and R1 can be used. A 16-bit external memory addressing is supported by eight 16-bit
datapointers. Registers XPAGE and SYSCON are controlling whether data fetches at
addresses F800
Internal Data Memory
The internal data memory is divided into four physically distinct blocks:
– the lower 128 bytes of RAM including four banks containing eight registers each
– the upper 128 byte of RAM
– the 128 byte special function register area.
– a 2 K 8 area which is accessed like external RAM (MOVX-instructions), implemented on
A mapping of the internal data memory is also shown in figure 2. The overlapping address
spaces are accessed by different addressing modes (see User's Manual SAB 80C517). The
stack can be located anywhere in the internal data memory.
Architecture for the XRAM
The contents of the XRAM is not affected by a reset or HW Power Down. After power-up the
contents is undefined, while it remains unchanged during and after a reset or HW Power Down
if the power supply is not turned off.
The additional On-Chip RAM is logically located in the "external data memory" range at the
upper end of the 64 Kbyte address range (F800
(only by reset) the XRAM. If it is disabled the device shows the same behaviour as the parts
without XRAM, i.e. all MOVX accesses use the external bus to physically external data
memory.
Semiconductor Group
chip at the address range from F800
controls whether data is read or written to XRAM or external RAM.
H
to FFFF
H
are done from internal XRAM or from external data memory.
H
to FFFF
19
H
-FFFF
H
. Special Function Register SYSCON
H
). It is possible to enable and disable
SAB 80C517A/83C517A-5
1994-05-01