Datasheet

Section 6 Bus Controller
Rev. 4.00 Sep 27, 2006 page 175 of 1130
REJ09B0327-0400
6.5.3 Wait Control
As with the basic bus interface, either program wait insertion or pin wait insertion using the WAIT
pin can be used in the initial cycle (full access) of the burst ROM interface. See section 6.4.5, Wait
Control.
Wait states cannot be inserted in a burst cycle.
6.6 Idle Cycle
6.6.1 Operation
When this LSI chip accesses external space, it can insert a 1-state idle cycle (T
I
) between bus
cycles when a write cycle occurs immediately after a read cycle. By inserting an idle cycle it is
possible, for example, to avoid data collisions between ROM, with a long output floating time, and
high-speed memory, I/O interfaces, and so on.
If an external write occurs after an external read while the ICIS0 bit in BCR is set to 1, an idle
cycle is inserted at the start of the write cycle. This is enabled in advanced mode and normal
mode.
Figure 6.15 shows an example of the operation in this case. In this example, bus cycle A is a read
cycle from ROM with a long output floating time, and bus cycle B is a CPU write cycle. In (a), an
idle cycle is not inserted, and a collision occurs in cycle B between the read data from ROM and
the CPU write data. In (b), an idle cycle is inserted, and a data collision is prevented.