SH7205 Datasheet, PDF (391/1904 Pages) Renesas Technology Corp – Renesas 32-Bit RISC Microcomputer SuperHTM RISC engine Family / SH7200 Series

Section 10 Bus State Controller (BSC)
10.7 Usage Notes
10.7.1 Write Buffer
In writing to locations in normal space or in SDRAM space, data to be written are held once in the
internal write buffer of the BSC, after which writing to the device connected in external space or
SDRAM space (external device) proceeds. Since writing of data from the write buffer to the
external device is automatic, no processing by software is required.
At the same time, care is required on the following point. Writing by the CPU or DMAC appears
to be complete at the point where the data are stored in the write buffer mentioned above. In other
words, at the point where writing by the CPU or DMAC is completed, writing to the external
device may in some cases not have been completed. To confirm completion of writing to the
external device, execute dummy reading from the normal space or SDRAM space. Completion of
dummy reading guarantees the completion of writing to the external device for previous write-
access. The target device for dummy reading need not be the same as the target for writing.
Furthermore, the space need not be the same.
10.7.2 Point for Caution at the Time of a Transition to Software Standby or Deep
Standby Mode
In cases where a transition to software standby or deep standby mode follows the execution of
writing to locations in normal space or in SDRAM space, data may remain within the internal
write buffer of the BSC. To ensure that data do not remain within the write buffer, execute dummy
reading from an external device in the same way as described above.
Rev. 1.00 Mar. 25, 2008 Page 359 of 1868
REJ09B0372-0100