DS72011RB120FPV datasheet(313/1196 Pages) RENESAS

313 / 1196 page

Section 9 Bus State Controller (BSC)

Rev. 2.00 Sep. 07, 2007 Page 285 of 1164

REJ09B0321-0200

9.6

Usage Note

9.6.1

Note on Power-on Reset Exception Handling and Deep Standby Mode Cancellation

When writing to the external address space or making SDRAM settings in power-on reset

exception handling or cancellation of deep standby mode, be sure to set bits ACOSW[3:0] in

ACSWR to B'0011 beforehand.

9.6.2

Write Buffer

In write access to normal or SDRAM space, the write data are stored once in the internal write

buffer of the BSC, and only after that does actual writing to the device (external device) connected

in the normal or SDRAM space proceed. Since writing from the write buffer to the external device

is performed automatically, no processing by software is necessary.

However, care must be taken on the following point. Write access from the CPU or DMAC

appears complete at the point where the data are stored in the above write buffer. That is, at the

point where the write access from the CPU or DMA controller has been completed, writing to the

external device might not have been completed. To confirm the completion of writing to the

external device, dummy read the normal or SDRAM space. Completion of the dummy-read

operation guarantees the completion of writing to the external device in response to previous write

access. The target address for the dummy read operation does not have to be in the same device as

the target for write access. Furthermore, it does not have to be in the same space.

9.6.3

Note on Transition to Software Standby Mode or Deep Standby Mode

When a transition to software standby mode or deep standby mode is made after write access to

the normal or SDRAM space, there is a possibility that data remains in the internal write buffer of

the BSC. To confirm that no data remain in the write buffer, execute a dummy read of the external

device in the same way as described above.

DS72011RB120FPV Datasheet(PDF) 313 Page - Renesas Technology Corp