HD6417615 Hitachi Semiconductor, HD6417615 Datasheet - Page 294

• Manufacturer Part Number: HD6417615
• Description: Hardware Manual
• Manufacturer: Hitachi Semiconductor

7.3.2
The chip provides a conversion function in CS2, CS4 space for connection to and to maintain data
compatibility with devices that use little-endian format (in which the LSB is the 0 position in the
byte data lineup). When the endian specification bit of BCR1 is set to 1, CS2, CS4 space is little-
endian. The relationship between device data width and access unit for little-endian format is
shown in figures 7.5, 7.6, and 7.7. When sharing memory or the like with a little-endian bus
master, the SH7615 connects D31–D24 to the least significant byte (LSB) of the other bus master
and D7–D0 to the most significant byte (MSB), when the bus width is 32 bits. When the width is
16 bits, the SH7615 connects D15–D8 to the least significant byte of the other bus master and D7–
D0 to the most significant byte.
Only data conversion is supported by this function. For this reason, be careful not to place
program code or constants in the CS2, CS4 space. When this function is used, make sure that the
access unit is the same for writing and reading. For example, data written by longword access
should be read by longword access. If the read access unit is different from the write access unit,
an incorrect value will be read.
A24–A0
000000
000001
000002
000003
000000
000002
000000
Connection to Little-Endian Devices
D31
7
7
7
A24–A0
000000
000001
000002
000003
000000
000002
000000
000002
Figure 7.5 32-Bit External Devices and Their Access Units
Figure 7.6 16-Bit External Devices and Their Access Units
32-bit external device (little-endian)
16-bit external device (little-endian)
0
0
0
D15
D23
23
7
7
7
7
15
15
7
7
16
0
0
0
0 15
0 15
0
8
8
D7
D15
15
7
7
31
7
7
23
24
D0
16 31
0
0
8
8
8
0
0 15
D7
7
Data input/output pin
Byte read/write of address 0
Byte read/write of address 1
Byte read/write of address 2
Byte read/write of address 3
Word read/write of address 0
Word read/write of address 2
Longword read/write of address 0
24
D0
0
8
Data input/output pin
Byte read/write of address 0
Byte read/write of address 1
Byte read/write of address 2
Byte read/write of address 3
Word read/write of address 0
Word read/write of address 2
Longword read/write of address 0
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