r8a77850anbg Renesas Electronics Corporation., r8a77850anbg Datasheet - Page 545

• Manufacturer Part Number: r8a77850anbg
• Description: Renesas 32-bit Risc Microcomputer Superh? Risc Engine Family
• Manufacturer: Renesas Electronics Corporation.

command to be issued at time 2 from the following request queue. From the search results it is
seen that advance precharge processing can be executed for the third read (8-byte) request and the
fourth read (16-byte) request. Because the DBSC2 gives priority to preceding requests, it decides
to perform advance precharge processing for the third read (8-byte) request, and issues a PRE
command to the SDRAM.
When the time advances to time 3, the ACT command cannot be issued for the first read (16-byte)
request at time 3 either, and so a search of the following queue is performed for a command which
can be issued. Due to timing constraints, the ACT command cannot be issued for the third read (8-
byte) request, and as a result, issuance of the PRE command corresponding to the fourth read (16-
byte) request is selected.
At time 4, it is possible to execute request processing for the first read (16-byte) request, and an
ACT command is issued to the DDR2-SDRAM.
Thereafter, the processing described above is repeated.
Request
No.
1
2
3
4
SDRAM command
Read (16 bytes)
Read (32 bytes)
Read (8 bytes)
Read (16 bytes)
Request
Figure 12.6 Example of Preceding Precharge/Activate Processing
Bank to be
accessed
Bank 0
Bank 1
Bank 2
Bank 3
Page state
during request
Miss
Hit
Miss
Miss
As the burst length is 4 in the DDR2-SDRAM, the interval between READ commands is always two cycles.
PRE
PRE PRE
Time Time Time Time Time Time Time Time Time Time Time Time Time Time Time
1
PRE
2
PRE ACT
PRE
3
ACT
4
5
ACT READ ACT READ
ACT
6
READ
Rev.1.00 Jan. 10, 2008 Page 515 of 1658
7
ACT
12. DDR2-SDRAM Interface (DBSC2)
8
READ
9
10
READ
READ
11
12
REJ09B0261-0100
READ
READ
13
14
READ
READ
15