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XC2200 Derivatives
System Units (Vol. 1 of 2)
Memory Organization
User’s Manual
3-71
V2.1, 2008-08
MemoryX2K, V1.3
Both are supplied by the wake-up power domain (DMP_M) and retain their data while
the system power domain (DMP_1) is switched off.
3.11.1
Stand-By RAM Accesses
The SBRAM is not mapped into the address range of the processor. All accesses are
done via the 4 SFRs SBRAM_WADD, SBRAM_RADD, SBRAM_DATA0 and
SBRAM_DATA1. The following access options exist:
•
Write without automatic increment of the write address pointer:
The SW has to write the target address first to WADD and then the data to DATA0.
The data written to DATA0 is transferred to the indicated address in the SBRAM if (at
least) the lower byte of DATA0 is written. If DATA0 is written again the same address
in SBRAM is used for data storage. Bit WADD.MOD is cleared by a write access to
DATA0.
•
Write with automatic increment of the write address pointer:
The SW has to write the first target address to WADD and thereafter the data block
can be written word by word to DATA1. The data written to DATA1 is transferred to
the indicated address in the SBRAM if (at least) the lower byte of SRDR1 is written.
In parallel to the data storage in the SBRAM, the write address pointer WADD.WPTR
is automatically incremented by 1 (one word) for the next data to be stored. The
address pointer automatically does a wrap-around after reaching its maximum value
and in this case, bit WADD.WA is set. Bit WADD.MOD is set by a write access to
DATA1.
•
Read without automatic increment of the read address pointer:
The SW has to write the target address first to RADD and then can read the data from
DATA0. If DATA0 is read again the same address in SBRAM is read out. Bit
RADD.MOD is cleared by a read access to DATA0.
•
Read with automatic increment of the read address pointer:
The SW has to write the first target address to RADD and can then read the data
block word by word from DATA1. In parallel to the read action from SBRAM, the read
address pointer RADD.RPTR is automatically incremented by 1 (one word) for the
next data to be read. The address pointer automatically does a wrap-around after
reaching its maximum value and in this case, bit RADD.WA is set. Bit RADD.MOD is
set by a read access to DATA1.
The automatic increment accesses allow performing back-to-back data writes and
reads.
Note: Because read accesses to SBRAM_DATA0 and SBRAM_DATA1 return the value
that has been pre-read upon the most recent update of register SBRAM_RADD,
any data written to location @SBRAM_RADD can only be read back after
SBRAM_RADD has been updated with the very same address (either explicitly by
writing to it or implicitly via the auto-increment function). Generally when switching