Bus Arbitration - Hitachi SH7709S Hardware Manual

T1
CKIO
A25 to A0
CSm
CSn
BS
RD/WR
RD
D31 to D0
Area m read
Area m inter-access wait specification
10.3.8

Bus Arbitration

When a bus release request (BREQ) is asserted 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 or write-back, or TAS instruction execution between
the read cycle and write cycle. Bus arbitration is not executed in multiple bus cycles that are
generated when the data bus width is shorter than the access size; i.e. in the bus cycles when
longword access is executed for the 8-bit memory. At the negation of BREQ, BACK is negated
and bus use is restarted. See Appendix A.1, Pin States, for the pin states when the bus is released.
The SH7709S sometimes needs to retrieve a bus it has released. For example, when memory
generates a refresh request or an interrupt request internally, the SH7709S must perform the
appropriate processing. The SH7709S 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 SH7709S retrieves the bus and carries out the processing.
T2 Twait T1
Area n space read
Figure 10.42 Waits between Access Cycles
T2 Twait T1
Area n space write
Area n inter-access wait specification
T2
325