SH7708 datasheet(314/633 Pages) RENESAS

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296

CKIO

CSm

CSn

A25 to A0

RD/

D31 to D0

Twait

Area m read

Area m inter-access wait specification

Area n inter-access wait specification

Area n space read

Area n space write

Figure 10.50 Waits between Access Cycles

10.3.10

Bus Arbitration

When a bus release request (

BREQ) is received from an external device, buses are released after

the bus cycle being executed is completed and a bus grant signal (

BACK) is output. The bus is not

released during burst transfers for cache fills. In the case of multiple bus cycles generated because

the data bus width is smaller than the access size—for example, in longword access to 8-bit-wide

memory—bus arbitration is not performed between bus cycles. At the negation of

BREQ, BACK

is negated and bus use is restarted. See Appendix B, Pin States, for the pin status when the bus is

released.

The SH7708 Series sometimes needs to retrieve a bus it has released. For example, when memory

generates a refresh request or an interrupt request internally, the SH7708 Series must perform the

appropriate processing. The SH7708 Series has a bus request signal (

IRQOUT) for this purpose.

When it must retrieve the bus, it asserts the

IRQOUT signal. Devices asserting an external bus

release request receive the assertion of the

IRQOUT signal and negate the BREQ signal to release

the bus. The SH7708 Series retrieves the bus and carries out the processing.

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