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151
D15
7
0
D7
D0
7
7
7
23
8
8
8
7
0
7
0
0
0
0
7
15
15
15
31
16
0
A26–A0
000000
000001
000002
000003
000000
000002
000000
000002
16-bit device 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
Figure 7.6 16-Bit External Devices and Their Access Units (Little-Endian Format)
Using the Little-Endian Function:
The SH7604 normally uses big-endian alignment for data
input and output, but an endian conversion function is provided for the CS2 space to enable
connection to little-endian devices. The following two points should be noted when using this
function:
Little endian alignment should be used in the CS2 through-area.
When data is shared with another little-endian device using this function, the same access size
must be used by both. For example, to read data written in longword size by another little-
endian device, the SH7604 must use longword read access.
7.4
Accessing Ordinary Space
7.4.1
Basic Timing
A strobe signal is output by ordinary space accesses of CS0–CS3 spaces to provide primarily for
SRAM direct connections. Figure 7.7 shows the basic timing of ordinary space accesses. Ordinary
accesses without waits end in 2 cycles. The
BS
signal is asserted for 1 cycle to indicate the start of
the bus cycle. The
CSn
signal is negated by the fall of clock T2 to ensure the negate period. The
negate period is thus half a cycle when accessed at the minimum pitch.
The access size is not specified during a read. The correct access start address will be output to the
LSB of the address, but since no access size is specified, the read will always be 32 bits for 32-bit
devices and 16 bits for 16-bit devices. For writes, only the
WE
signal of the byte that will be
written is asserted. For 32-bit devices,
WE3
specifies writing to a 4n address and
WE0
specifies
writing to a 4n+3 address. For 16-bit devices,
WE1
specifies writing to a 2n address and
WE0
specifies writing to a 2n+1 address. For 8-bit devices, only
WE0
is used.
The
RD
signal must be used to control data output of external devices so that conflicts do not
occur between trace information for emulators or the like output from the SH7604 and external
device read data. In other words, when data buses are provided with buffers, the
RD
signal must
be used for data output in the read direction. When RD/
WR
signals do not perform accesses, the