RX610 Group
11. Buses
R01UH0032EJ0120 Rev.1.20
Page 279 of 1006
Feb 20, 2013
11.4
Endian and Data Alignment
Eight, 16, and 32 bits are the units of access by the CPU and other internal bus-master modules. The external bus
controller has a data-alignment facility, and this can control whether access is to bits D15 to D8 or to bits D7 to D0, the
bus specification (8-bit or 16-bit bus space), the unit of access, and the endian for areas of the external address space.
11.4.1
16-Bit Bus Space
When a 16-bit width is selected for a bus space by the BSIZE[1:0] bits in CSiCNT, the address bus (A23 to A1) output
signals for access to 16-bit units are enabled, but the A0 signal is always 0.
When byte strobe mode (the WRMOD bit = 0 in CSiMOD) is selected, the WRi# (i = 0, 1) pins are enabled, but the BCi#
(i = 0, 1) pins are not used.
When single write strobe mode (the WRMOD bit = 1 in CSiMOD) is selected, the WR# pin is enabled and always
outputs the low level during write access, regardless of the unit of access. The valid byte position is indicated by the
BCi# (i = 0, 1) pins. The WRi# (i = 0, 1) pins are not used.
Page access can occur in access to data in 32-bit units. The situations in which page access occurs are indicated by the
letter "(p)" in figures 11.3 and 11.4.
The valid positions of data external to the chip and of control signals differ according to whether the endian is big or
little.
Data Size
8 bits
16 bits
32 bits
Access
Address
Number of
Access
4n
One
Two
D0
D7
D15
Data Bus
RD#
WR1#/BC1#
WR0#/BC0#
Bus Cycle
Unit of Data
First
First
8 bits
8 bits
8 bits
4n+1
One
First
8 bits
4n
First
One
4n+1
4n
4n+2
One
First
8 bits
4n+3
One
First
8 bits
Two
First
8 bits
8 bits
4n+2
First
One
4n+3
First
First
Second
Third
4n+1
Two
Three
4n+2
First
First
Third
4n+3
Two
Three
Address
4n
4n
4n+2
4n+2
4n
4n
4n+2
4n+2
4n+2
4n+4
4n
4n+2
4n
4n+2
4n+4
4n+2
4n+4
4n+2
4n+4
4n+6
[Legend]
(p): Page access (only when page access is enabled with the PRENB and PWENB bits in CSiMOD)
16
23
24
31
8
15
0
7
0
7
0
7
0
7
0
7
0
7
8
15
8
15
0
7
0
7
8
15
8
15
0
7
0
7
8
15
16
23
24
31
8
15
0
7
16
23
24
31
0
7
8
15
16
23
24
31
(p)
D8
Second
Second
Second
Second
Second
16 bits
16 bits
16 bits
16 bits
16 bits
8 bits
8 bits
16 bits
16 bits
16 bits
8 bits
8 bits
Figure 11.3 Data Alignment (Little Endian) in 16-Bit Bus Space