C165_96 Datasheet, PDF (220/283 Pages) Siemens Semiconductor Group – 16-Bit CMOS Single-Chip Microcontrollers

10Jul97@15:33h
The Synchronous Serial Port / C163
Accessing the SSP
The SSP is implemented as an X-Peripheral and is therefore accessed like an external memory or
peripheral. That means that the registers of the SSP can be read and written using 16-bit or 8-bit
direct or indirect MEM addressing modes. Since the XBUS, to which the SSP is connected, also
represents the external bus, SSP accesses follow the same rules and procedures as accesses to
the external bus. SSP accesses cannot be executed in parallel to external instruction fetches or
data read/writes, but are arbitrated and inserted into the external bus access stream.
Accesses to the SSP use demultiplexed addresses and a 16-bit data bus (byte accesses possible).
An access time of 100 ns @ 20 MHz CPU clock is provided using no waitstates.
The SSP address area starts at 00’EF00_H and covers 256 Bytes. A dedicated hardwired XADRS/
XBCON register pair selects the respective address window, so none of the programmable register
pairs must be sacrificed in order to access the SSP.
Locating the SSP address area to address 00’EF00_H in segment 0 has the advantage that the SSP
is accessible via data page 3, which is the 'system' data page, accessed usually through the
'system' data page pointer DPP3. In this way, the internal addresses, such like SFRs, internal RAM,
and the SSP registers, are all located within the same data page and form a contiguous address
space.
Semiconductor Group
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