4.3.6
RAM Mode
Setting CCR.ORA to 1 enables half of the operand cache to be used as RAM. In the SH7750 or
SH7750S, the 8 kbytes of operand cache entries 128 to 255 and 384 to 511 are used as RAM. In
the SH7750/SH7750S-compatible mode of the SH7750R, the 8-kbyte area otherwise used for OC
entries 256 to 511 is designated as a RAM area. In the double-sized cache mode of the SH7750R,
a total of 16 kbytes, comprising entries 256 to 511 in both of the ways of the operand cache, is
designated as a RAM area. Other entries can still be used as cache. RAM can be accessed using
addresses H'7C00 0000 to H'7FFF FFFF. Byte-, word-, longword-, and quadword-size data reads
and writes can be performed in the operand cache RAM area. Instruction fetches cannot be
performed in this area. With the SH7750R, the OC index mode is not available in RAM mode.
An example of RAM use in the SH7750 or SH7750S is shown below. Here, the 4 kbytes
comprising OC entries 128 to 255 are designated as RAM area 1, and the 4 kbytes comprising OC
entries 384 to 511 as RAM area 2.
•
When OC index mode is off (CCR.OIX = 0)
H'7C00 0000 to H'7C00 0FFF (4 kB): Corresponds to RAM area 1
H'7C00 1000 to H'7C00 1FFF (4 kB): Corresponds to RAM area 1
H'7C00 2000 to H'7C00 2FFF (4 kB): Corresponds to RAM area 2
H'7C00 3000 to H'7C00 3FFF (4 kB): Corresponds to RAM area 2
H'7C00 4000 to H'7C00 4FFF (4 kB): Corresponds to RAM area 1
:
:
:
RAM areas 1 and 2 in the SH7750 or SH7750S then repeat every 8 kbytes up to H'7FFF FFFF.
Thus, to secure a continuous 8-kbyte RAM area, the area from H'7C00 1000 to H'7C00 2FFF
can be used, for example.
•
When OC index mode is on (CCR.OIX = 1)
H'7C00 0000 to H'7C00 0FFF (4 kB): Corresponds to RAM area 1
H'7C00 1000 to H'7C00 1FFF (4 kB): Corresponds to RAM area 1
H'7C00 2000 to H'7C00 2FFF (4 kB): Corresponds to RAM area 1
:
:
:
H'7DFF F000 to H'7DFF FFFF (4 kB): Corresponds to RAM area 1
H'7E00 0000 to H'7E00 0FFF (4 kB): Corresponds to RAM area 2
H'7E00 1000 to H'7E00 1FFF (4 kB): Corresponds to RAM area 2
:
:
:
H'7FFF F000 to H'7FFF FFFF (4 kB): Corresponds to RAM area 2
As the distinction between RAM areas 1 and 2 is indicated by address bit [25], the area from
H'7DFF F000 to H'7E00 0FFF should be used to secure a continuous 8-kbyte RAM area.
Rev. 6.0, 07/02, page 106 of 986
RENESAS [ RENESAS TECHNOLOGY CORP ]
