Endianess, Endianess -4 – Cirrus Logic EP73xx User Manual
Page 78
6-4
EP7309/11/12 User’s Manual - DS508UM4
Copyright Cirrus Logic, Inc. 2003
Processor Support
6
Endianess
The EP73xx uses little endian configuration for the internal registers. However, it is
possible to connect to a big endian external memory device. The big-endian/little-
endian bit in the internal registers sets whether the EP73xx treats words in memory as
being stored in big endian or little endian format.
• Big endian - least significant byte (LSB) read as most significant byte (MSB)
• Little endian - LSB read as LSB
Note: dc = don’t care
Bold indicates active byte lane.
Table 6-4: Effect of Endianess on Read Operations
Address
(W/B)
Data in
Memory
(as seen
by the
EP73xx)
Byte Lanes to Memory/Ports/Registers
R0 Contents
Big Endian Memory
Little Endian Memory
7:0
15:8
23:16
31:24
7:0
15:8
23: 16
31: 24
Big Endian
Little
Endian
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 (H)
11223344
44
33
22
11
44
33
22
11
00001122
00003344
Word + 1(H)
11223344
44
33
22
11
44
33
22
11
220000011
44000033
Word + 2(H)
11223344
44
33
22
11
44
33
22
11
00003344
00001122
Word + 3(H)
11223344
44
33
22
11
44
33
22
11
44000033
22000011
Word + 0 (B)
11223344
dc
dc
dc
11
44
dc
dc
dc
00000011
00000044
Word + 1 (B)
11223344
dc
dc
22
dc
dc
33
dc
dc
00000022
00000033
Word + 2 (B)
11223344
dc
33
dc
dc
dc
dc
22
dc
00000033
00000022
Word + 3 (B)
11223344
44
dc
dc
dc
dc
dc
dc
11
00000044
00000011
Table 6-5: Effect on Endianess on 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 (H)
11223344
44
33
44
33
44
33
44
33
Word + 1 (H)
11223344
44
33
44
33
44
33
44
33