Section 8 Bus State Controller (BSC)
Rev. 5.00 May 29, 2006 page 247 of 698
REJ09B0146-0500
8.5.7
Waits between Access Cycles
A problem associated with higher external memory bus operating frequencies is that data buffer
turn-off on completion of a read from a low-speed device may be too slow, causing a collision
with data in the next access. This results in lower reliability or incorrect operation. To avoid this
problem, a data collision prevention feature has been provided. This memorizes the preceding
access area and the kind of read/write. If there is a possibility of a bus collision when the next
access is started, a wait cycle is inserted before the access cycle thus preventing a data collision.
There are two cases in which a wait cycle is inserted: when an access is followed by an access to a
different area, and when a read access is followed by a write access from this LSI. When this LSI
performs consecutive write cycles, the data transfer direction is fixed (from this LSI to other
memory) and there is no problem. With read accesses to the same area, in principle, data is output
from the same data buffer, and wait cycle insertion is not performed. Bits AnIW1 and AnIW0 (n =
0, 2 to 6) in WCR1 specify the number of idle cycles to be inserted between access cycles when a
physical space area access is followed by an access to another area, or when this LSI performs a
write access after a read access to physical space area n. If there is originally space between
accesses, the number of idle cycles inserted is the specified number of idle cycles minus the
number of empty cycles.
Waits are not inserted between accesses when bus arbitration is performed, since empty cycles are
inserted for arbitration purposes.
Summary of Contents for SH7706 Series
Page 8: ...Rev 5 00 May 29 2006 page viii of xlviii ...
Page 160: ...Section 5 Cache Rev 5 00 May 29 2006 page 112 of 698 REJ09B0146 0500 ...
Page 370: ...Section 11 Watchdog Timer WDT Rev 5 00 May 29 2006 page 322 of 698 REJ09B0146 0500 ...
Page 554: ...Section 17 Pin Function Controller PFC Rev 5 00 May 29 2006 page 506 of 698 REJ09B0146 0500 ...
Page 576: ...Section 18 I O Ports Rev 5 00 May 29 2006 page 528 of 698 REJ09B0146 0500 ...
Page 746: ...Index Rev 5 00 May 29 2006 page 698 of 698 REJ09B0146 0500 ...
Page 749: ...SH7706 Group Hardware Manual ...