SH7014 datasheet(174/754 Pages) RENESAS

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8. Bus State Controller (BSC)

Rev.5.00 Sep. 27, 2007 Page 140 of 716

REJ09B0398-0500

8.6

Waits between Access Cycles

When a read from a slow device is completed, data buffers may not go off in time to prevent data

conflicts with the next access. If there is a data conflict during memory access, the problem can be

solved by inserting a wait in the access cycle.

To enable detection of bus cycle starts, waits can be inserted between access cycles during

continuous accesses of the same CS space by negating the

CSn signal once.

8.6.1

Prevention of Data Bus Conflicts

For the two cases of write cycles after read cycles, and read cycles for a different area after read

cycles, waits are inserted so that the number of idle cycles specified by the IW31 to IW00 bits of

the BCR2 and the DIW of the DCR occur. When idle cycles already exist between access cycles,

only the number of empty cycles remaining beyond the specified number of idle cycles are

inserted.

Figure 8.20 shows an example of idles between cycles. In this example, 1 idle between CSn space

cycles has been specified, so when a CSm space write immediately follows a CSn space read

cycle, 1 idle cycle is inserted.

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