HD6417705 Datasheet, PDF (281/739 Pages) Renesas Technology Corp – Renesas 32-Bit RISC Microcomputer SuperH RISC engine Family/SH7700 Series

7.11 Wait between Access Cycles
As the operating frequency of LSIs becomes higher, the off-operation of the data buffer often
collides with the next data access when the read operation from devices with slow access speed is
completed. As a result of these collisions, the reliability of the device is low and malfunctions may
occur. A function that avoids data collisions by inserting wait cycles between continuous access
cycles has been newly added.
The number of wait cycles between access cycles can be set by bits IWW[1:0], IWRWD[1:0],
IWRWS[1:0], IWRRD[1:0], and IWRRS[1:0] in CSnBCR, and bits DMAIW[1:0] and DMAIWA
in CMNCR. The conditions for setting the wait cycles between access cycles (idle cycles) are
shown below.
1. Continuous accesses are write-read or write-write
2. Continuous accesses are read-write for different spaces
3. Continuous accesses are read-write for the same space
4. Continuous accesses are read-read for different spaces
5. Continuous accesses are read-read for the same space
6. Data output from an external device caused by DMA single transfer is followed by data output
from another device that includes this LSI (DMAIWA = 0)
7. Data output from an external device caused by DMA single transfer is followed by any type of
access (DMAIWA = 1)
7.12 Bus Arbitration
This LSI supports bus arbitration. This LSI has bus mastership in the normal state and releases bus
mastership after receiving a bus request from another device.
To prevent device malfunction while the bus mastership is transferred between master and slave,
the LSI negates all of the bus control signals before bus release. When the bus mastership is
received, all of the bus control signals are first negated and then driven appropriately. In this case,
output buffer conflicts can be prevented because the master and slave drive the same signals with
the same values. In addition, to prevent noise while the bus control signal is in the high-impedance
state, pull-up resistors must be connected to these control signals.
Bus mastership is transferred at the boundary of bus cycles. Namely, bus mastership is released
immediately after receiving a bus request when a bus cycle is not being performed. The release of
bus mastership is delayed until the bus cycle is complete when a bus cycle is in progress. Even
when from outside the LSI it looks like a bus cycle is not being performed, a bus cycle may be
performing internally, started by inserting wait cycles between access cycles. Therefore, it cannot
be immediately determined whether or not bus mastership has been released by looking at the CSn
signal or other bus control signals. The states that do not allow bus mastership release are shown
below.
Rev. 2.00, 09/03, page 235 of 690