Renesas HD6417641, Hardware Manual, Page: 418 / 1036

Section 12 Bus State Controller (BSC)
Rev. 4.00 Sep. 14, 2005 Page 368 of 982
REJ09B0023-0400
Relationship between Refresh Requests and Bus Cycles: If a refresh request occurs during bus
cycle execution, the refresh cycle must wait for the bus cycle to be completed. If a refresh request
occurs while the bus is released by the bus arbitration function, the refresh will not be executed
until the bus mastership is acquired.
If a new refresh request occurs while waiting for the previous refresh request, the previous refresh
request is deleted. To refresh correctly, a bus cycle longer than the refresh interval or the bus
mastership occupation must be prevented from occurring. If a bus mastership is requested during
self-refresh, the bus will not be released until the refresh is completed.
Low-Frequency Mode: When the SLOW bit in SDCR is set to 1, output of commands, addresses,
and write data, and fetch of read data are performed at a timing suitable for operating SDRAM at a
low frequency.
Figure 12.31 shows the access timing in low-frequency mode. In this mode, commands, addresses,
and write data are output in synchronization with the falling edge of CKIO, which is half a cycle
delayed than the normal timing. Read data is fetched at the rising edge of CKIO, which is half a
cycle faster than the normal timing. This timing allows the hold time of commands, addresses,
write data, and read data to be extended.
If SDRAM is operated at a high frequency with the SLOW bit set to 1, the setup time of
commands, addresses, write data, and read data are not guaranteed. Take the operating frequency
and timing design into consideration when making the SLOW bit setting.