SH7672 datasheet(310/1292 Pages) RENESAS

310 / 1292 page

Section 7

Bus State Controller (BSC)

Rev. 1.00 Nov. 14, 2007 Page 284 of 1262

REJ09B0437-0100

7.5.8

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 idle (wait) cycles between continuous

access cycles has been newly added.

The number of wait cycles between access cycles can be set by the WM bit in CSnWCR, bits

IWW2 to IWW0, IWRWD2 to IWRWD0, IWRWS2 to IWRWS0, IWRRD2 to IWRRD0, and

IWRRS2 to IWRRS 0 in CSnBCR, and bits DMAIW2 to DMAIW0 and DMAIWA in CMNCR.

The conditions for setting the idle cycles between access cycles are shown below.

1. Continuous access cycles are write-read or write-write

2. Continuous access cycles are read-write for different spaces

3. Continuous access cycles are read-write for the same space

4. Continuous access cycles are read-read for different spaces

5. Continuous access cycles are read-read for the same space

6. Data output from an external device caused by DMA single address 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 address transfer is followed by any

type of access (DMAIWA = 1)

For the specification of the number of idle cycles between access cycles described above, refer to

the description of each register.

Besides the idle cycles between access cycles specified by the registers, idle cycles must be

inserted to interface with the internal bus or to obtain the minimum pulse width for a multiplexed

pin (

WEn). The following gives detailed information about the idle cycles and describes how to

estimate the number of idle cycles.

The number of idle cycles on the external bus from

CSn negation to CSn or CSm assertion is

described below. Here,

CSn and CSm also include CE2A and CE2B for PCMCIA.

There are eight conditions that determine the number of idle cycles on the external bus as shown

in table 7.20. The effects of these conditions are shown in figure 7.42.

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