r5s77631ay266bgv Renesas Electronics Corporation., r5s77631ay266bgv Datasheet - Page 469

• Manufacturer Part Number: r5s77631ay266bgv
• Description: Renesas 32-bit Risc Microcomputer Superhtm Risc Engine Family Sh-4a Series
• Manufacturer: Renesas Electronics Corporation.

Section 11 Local Bus State Controller (LBSC)
11.5.8
Wait Cycles between Accesses
A problem associated with higher operating frequencies for external memory buses is that the data
buffer turn-off after completion of a read from a low-speed device may be too slow, causing a
collision with the data in the next access, and resulting in lower reliability or malfunctions. To
prevent this problem, this module provides a data collision prevention function. It stores the
preceding access area and the type of read/write and inserts a wait cycle before the access cycle if
there is a possibility of a bus collision when the next access is started. The process for wait cycle
insertion consists of inserting idle cycles between the access cycles as shown in section 11.4.3,
CSn Bus Control Register (CSnBCR). If bits IWW, IWRWD, IWRWS, IWRRD and IWRRS in
CSnBCR (n = 0 to 2 and 4 to 6) are used to set the number of idle cycles between accesses, the
number of inserted idle cycles is only the specified number of idle cycles minus the number of idle
cycles specified by the bits.
When bus arbitration is performed, the bus is released after wait cycles are inserted between the
cycles.
When a DMA transfer (dual address mode) is performed, wait cycles are inserted as set in
CSnBCR idle cycle bits.
When access the MPX interface area continuously after read access, 1 wait cycle is inserted even
if set the wait cycle to 0.
When the access size is 8-byte or 16-byte, wait cycles are inserted every 4-byte access.
Rev. 1.00 Oct. 01, 2007 Page 403 of 1956
REJ09B0256-0100