
September 1997
21
PRELIMINARY DATA BOOK v2.0
FUNCTIONAL DESCRIPTION
CL-PS7111
Low-Power System-on-a-Chip
3.3
Endian Functionality
The CL-PS7111 uses a little-endian configuration for internal registers. However, it is possible to connect
the device to a big-endian external memory system.
Table 3-1
and
Table 3-2
demonstrate the behavior of
the CL-PS7111 in big- and little-endian mode, including the effect of performing non-aligned word
accesses. The register definitions in
Chapter 5
define the behavior of the internal CL-PS7111 registers in
big-endian mode in more detail.
The NCAS[3:0] lines for DRAM must always be connected with the same byte lane regardless of the
endian functionality, so that NCAS[0] is connected with D[7:0], and NCAS[3] with D[31:24]. In a little-
endian system, NCAS[0] is asserted for a read/write to byte 0 of DRAM and in a big-endian system
NCAS[3] is asserted to access byte 0 of DRAM.
a
X indicates a ‘don’t care’ state.
Table 3-1.
Endian Functionality and Read Operations
Address
(W/B)
Data in
Memory
Byte Lanes to Memory/Ports/Registers
R0 Contents
Big-endian Memory
Little-endian Memory
Big-
endian
Little-
endian
7:0
15:8
23:16
31:24
7:0
15:8
23:16
31:24
Word + 0 (W)
11223344
44
33
22
11
44
33
22
11
11223344
11223344
Word + 1 (W)
11223344
44
33
22
11
44
33
22
11
44112233
44112233
Word + 2 (W)
11223344
44
33
22
11
44
33
22
11
33441122
33441122
Word + 3 (W)
11223344
44
33
22
11
44
33
22
11
22334411
22334411
Word + 0 (B)
11223344
X
a
X
X
11
44
X
X
X
00000011
00000044
Word + 0 (B)
11223344
X
X
22
X
X
33
X
X
00000022
00000033
Word + 0 (B)
11223344
X
33
X
X
X
X
22
X
00000033
00000022
Word + 0 (B)
11223344
44
X
X
X
X
X
X
11
00000044
00000011
Table 3-2.
Endian Functionality and Write Operations
Address (W/B)
Register Contents
Byte Lanes to Memory/Ports/Registers
Big-endian Memory
Little-endian Memory
7:0
15:8
23:16
31:24
7:0
15:8
23:16
31:24
Word + 0 (W)
11223344
44
33
22
11
44
33
22
11
Word + 1 (W)
11223344
44
33
22
11
44
33
22
11
Word + 2 (W)
11223344
44
33
22
11
44
33
22
11
Word + 3 (W)
11223344
44
33
22
11
44
33
22
11
Word + 0 (B)
11223344
44
44
44
44
a
44
44
44
44