Hitachi SH7750 Hardware Manual page 531

negated, BACK is negated and use of the bus is resumed. See Appendix E, Pin Functions, for the
pin states when the bus is released.
When a refresh request is generated, the SH7750 Series performs a refresh operation as soon as
the currently executing bus cycle ends. However, refresh operations are deferred during multiple
bus cycles generated because the data bus width is smaller than the access size (for example, when
performing longword access to 8-bit bus width memory) and during a 32-byte transfer such as a
cache fill or write-back, and also between read and write cycles during execution of a TAS
instruction, and between read and write cycles when DMAC dual address transfer is executed.
Refresh operations are also deferred in the bus-released state.
If the synchronous DRAM interface is set to the RAS down mode the PALL command is issued
before a refresh cycle occurs or before the bus is released by bus arbitration.
As the CPU in the SH7750 Series is connected to cache memory by a dedicated internal bus,
reading from cache memory can still be carried out when the bus is being used by another bus
master inside or outside the SH7750 Series. When writing from the CPU, an external write cycle
is generated when write-through has been set for the cache in the SH7750 Series, or when an
access is made to a cache-off area. There is consequently a delay until the bus is returned.
When the SH7750 Series wants to take back the bus in response to an internal memory refresh
request, it negates BACK. On receiving the BACK negation, the device that asserted the external
bus release request negates BREQ to release the bus. The bus is thereby returned to the SH7750
Series, which then carries out the necessary processing.
Rev. 6.0, 07/02, page 481 of 986