Section 9 Bus State Controller (BSC)
Rev. 0.50 May 18, 2006 Page 358 of 1588
REJ09B0313-0050
9.5.12
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 9.21. The effects of these conditions are shown in figure 9.54.
Содержание Single-Chip Microcomputer SH7203
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Страница 400: ...Section 9 Bus State Controller BSC Rev 0 50 May 18 2006 Page 370 of 1588 REJ09B0313 0050 ...
Страница 668: ...Section 11 Multi Function Timer Pulse Unit 2 MTU2 Rev 0 50 May 18 2006 Page 638 of 1588 REJ09B0313 0050 ...
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Страница 1598: ...Section 31 Electrical Characteristics Rev 0 50 May 18 2006 Page 1568 of 1588 REJ09B0313 0050 ...
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