SH7040 Datasheet, PDF (241/923 Pages) Renesas Technology Corp – Renesas 32-Bit Single-Chip RISC Microprocessor SuperH RISC engine Family/SH7040 Series(CPU Core SH-2)

10.6.2 Simplification of Bus Cycle Start Detection
For consecutive accesses of the same CS space, waits are inserted so that the number of idle cycles
designated by the CW3–CW0 bits of the BCR2 occur. However, for write cycles after reads, the
number of idle cycles inserted will be the larger of the two values defined by the IW and CW bits.
When idle cycles already exist between access cycles, waits are not inserted. Figure 10.21 shows
an example. A continuous access idle is specified for CSn space, and CSn space is consecutively
write accessed.
T₁
T₂
T_idle
T₁
T₂
CK
Address
CSn
RD
WRx
Data
CSn space access
Idle cycle
CSn space access
Figure 10.21 Same Space Consecutive Access Idle Cycle Insertion Example
10.7 Bus Arbitration
The SH7040 series has a bus arbitration function that, when a bus release request is received from
an external device, releases the bus to that device. It also has two internal bus masters, the CPU
and the DMAC, DTC. The priority ranking for determining bus right transfer between these bus
masters is:
Bus right request from external device > refresh > DTC > DMAC > CPU
However, during a read or write in DMAC dual address mode, a burst transfer, or indirect address
transfer mode operation, the DMAC continues operating even if a DTC request is received.
Through port register settings, IRQOUT is asserted to indicate that a CAS-before-RAS refresh
request for DRAM has been generated during release of bus rights to an external device. Use this
203