Renesas SH7641 - Manual (Page 405)

Section 12 Bus State Controller (BSC)
Rev. 4.00 Sep. 14, 2005 Page 355 of 982
REJ09B0023-0400
Burst Write: A burst write occurs in the following cases in this LSI.
• Access size in writing is larger than data bus width.
• Write-back of the cache
• 16-byte transfer in DMAC
This LSI always accesses SDRAM with burst length 1. For example, write access of burst length 1
is performed continuously 4 times to write 16-byte continuous data to the SDRAM that is
connected to a 32-bit data bus.
The relationship between the access size and the number of bursts is shown in table 12.14.
Figure 12.21 shows a timing chart for burst writes. In burst write, an ACTV command is output in
the Tr cycle, the WRIT command is issued in the Tc1, Tc2, and Tc3 cycles, and the WRITA
command is issued to execute an auto-precharge in the Tc4 cycle. In the write cycle, the write data
is output simultaneously with the write command. After the write command with the auto-
precharge is output, the Trw1 cycle that waits for the auto-precharge initiation is followed by the
Tap cycle that waits for completion of the auto-precharge induced by the WRITA command in the
SDRAM. Between the Trwl and the Tap cycle, a new command will not be issued to the same
bank. However, access to another CS space or another bank in the same SDRAM space is enabled.
The number of Trw1 cycles is specified by the TRWL1 and TRWL0 bits in the CS3WCR register.
The number of Tap cycles is specified by the WTRP1 and WTRP0 bits in the CS3WCR register.