SH7721 datasheet(426/1524 Pages) RENESAS

426 / 1524 page

Section 9

Bus State Controller (BSC)

Rev. 3.00 Jan. 18, 2008 Page 364 of 1458

REJ09B0033-0300

(5)

Burst Write

A burst write occurs in the following cases in this LSI.

1. Access size in writing is larger than data bus width.

2. Copyback of the cache

3. 16-byte transfer in DMAC (access to non-cacheable region)

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 9.18.

Figure 9.17 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. In 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 CS3WCR. The number of Tap cycles is

specified by the TRP1 and TRP0 bits in CS3WCR.

SH7721 Datasheet(PDF) 426 Page - Renesas Technology Corp