SAB80C515A-5 Datasheet, PDF (66/108 Pages) Siemens Semiconductor Group – 8-Bit CMOS Single-Chip Microcontroller Family

SAB 80C515A/83C515A-5
Data Memory ('Data Space')
The data memory space consists of an internal and an external memory space.The
SAB 80C515A contains another 1 Kbyte on On-Chip RAM additional to the 256-bytes internal
RAM of the base type SAB 80C515. This RAM is called XRAM ('extended RAM') 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 a 16-bit datapointer.
Registers XPAGE and SYSCON are controlling whether data fetches at addresses F800_H to
FBFF_H are done from internal XRAM or from external data memory.
Internal Data Memory
The internal data memory is divided into four physically distinct blocks:
– the lower 128 bytes of RAM including four register banks containing eight
registers each
– the upper 128 byte of RAM
– the 128 byte special function register area.
– a 1 K × 8 area which is accessed like external RAM (MOVX-instructions), implemented on
chip at the address range from F800_H to FBFF_H. Special Function Register SYSCON
controls whether data is read from or written to XRAM or external RAM.
A map of the internal data memory is shown in figure 2. The overlapping address spaces of the
standard internal data memory (256 byte) are accessed by different addressing modes (see
User's Manual SAB 80C515). The stack can be located anywhere in the internal data memory.
Architecture of 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_H-FBFF_H). Nevertheless when XRAM is
enabled the address range F800_H to FFFF_H is occupied. This is done to assure software
compatibility to SAB 80C517A. It is possible to enable and disable (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
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