SH7713 Datasheet, PDF (494/904 Pages) Renesas Technology Corp – Renesas 32-Bit RISC Microcomputer SuperHTM RISC engine Family / SH7700 Series

Section 12 Bus State Controller (BSC)
12.5.10 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. This LSI has a function that avoids data collisions by inserting wait cycles between
continuous access cycles.
The number of wait cycles between access cycles can be set by bits IWW[2:0], IWRWD[2:0],
IWRWS[2:0], IWRRD[2:0], and IWRRS[2:0] in CSnBCR, and bits DMAIW[2:0] 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)
12.5.11 Bus Arbitration
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 contention 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
Rev.1.50 Aug. 30, 2006 Page 454 of 860
REJ09B0288-0150