Section 9 Bus State Controller (BSC)
Rev. 0.50 May 18, 2006 Page 318 of 1588
REJ09B0313-0050
(7) Bank
Active
The SDRAM bank function can be used to support high-speed access to the same row address.
When the BACTV bit in SDCR is 1, access is performed using commands without auto-precharge
(READ or WRIT). This function is called bank-active function. This function is valid only for
either the upper or lower bits of area 3. When area 3 is set to bank-active mode, area 2 should be
set to normal space or SRAM with byte selection. When areas 2 and 3 are both set to SDRAM or
both the upper and lower bits of area 3 are connected to SDRAM, auto precharge mode must be
set.
When the bank-active function is used, precharging is not performed when the access ends. When
accessing the same row address in the same bank, it is possible to issue the READ or WRIT
command immediately, without issuing an ACTV command. As SDRAM is internally divided
into several banks, it is possible to activate one row address in each bank. If the next access is to a
different row address, a PRE command is first issued to precharge the relevant bank, then when
precharging is completed, the access is performed by issuing an ACTV command followed by a
READ or WRIT command. If this is followed by an access to a different row address, the access
time will be longer because of the precharging performed after the access request is issued. The
number of cycles between issuance of the PRE command and the ACTV command is determined
by the WTRP1 and WTPR0 bits in CS3WCR.
In a write, when an auto-precharge is performed, a command cannot be issued to the same bank
for a period of Trwl + Tap cycles after issuance of the WRITA command. When bank active mode
is used, READ or WRIT commands can be issued successively if the row address is the same. The
number of cycles can thus be reduced by Trwl + Tap cycles for each write.
There is a limit on tRAS, the time for placing each bank in the active state. If there is no guarantee
that there will not be a cache hit and another row address will be accessed within the period in
which this value is maintained by program execution, it is necessary to set auto-refresh and set the
refresh cycle to no more than the maximum value of tRAS.
A burst read cycle without auto-precharge is shown in figure 9.23, a burst read cycle for the same
row address in figure 9.24, and a burst read cycle for different row addresses in figure 9.25.
Similarly, a burst write cycle without auto-precharge is shown in figure 9.26, a burst write cycle
for the same row address in figure 9.27, and a burst write cycle for different row addresses in
figure 9.28.
In figure 9.24, a Tnop cycle in which no operation is performed is inserted before the Tc cycle that
issues the READ command. The Tnop cycle is inserted to acquire two cycles of CAS latency for
the DQMxx signal that specifies the read byte in the data read from the SDRAM. If the CAS
Содержание Single-Chip Microcomputer SH7203
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Страница 98: ...Section 2 CPU Rev 0 50 May 18 2006 Page 68 of 1588 REJ09B0313 0050 ...
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Страница 242: ...Section 8 Cache Rev 0 50 May 18 2006 Page 212 of 1588 REJ09B0313 0050 ...
Страница 400: ...Section 9 Bus State Controller BSC Rev 0 50 May 18 2006 Page 370 of 1588 REJ09B0313 0050 ...
Страница 668: ...Section 11 Multi Function Timer Pulse Unit 2 MTU2 Rev 0 50 May 18 2006 Page 638 of 1588 REJ09B0313 0050 ...
Страница 696: ...Section 13 Watchdog Timer WDT Rev 0 50 May 18 2006 Page 666 of 1588 REJ09B0313 0050 ...
Страница 726: ...Section 14 Realtime Clock RTC Rev 0 50 May 18 2006 Page 696 of 1588 REJ09B0313 0050 ...
Страница 796: ...Section 15 Serial Communication Interface with FIFO SCIF Rev 0 50 May 18 2006 Page 766 of 1588 REJ09B0313 0050 ...
Страница 876: ...Section 17 I2 C Bus Interface 3 IIC3 Rev 0 50 May 18 2006 Page 846 of 1588 REJ09B0313 0050 ...
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Страница 1054: ...Section 21 D A Converter DAC Rev 0 50 May 18 2006 Page 1024 of 1588 REJ09B0313 0050 ...
Страница 1226: ...Section 23 USB 2 0 Host Function Module USB Rev 0 50 May 18 2006 Page 1196 of 1588 REJ09B0313 0050 ...
Страница 1294: ...Section 24 LCD Controller LCDC Rev 0 50 May 18 2006 Page 1264 of 1588 REJ09B0313 0050 ...
Страница 1386: ...Section 26 I O Ports Rev 0 50 May 18 2006 Page 1356 of 1588 REJ09B0313 0050 ...
Страница 1512: ...Section 30 List of Registers Rev 0 50 May 18 2006 Page 1482 of 1588 REJ09B0313 0050 ...
Страница 1598: ...Section 31 Electrical Characteristics Rev 0 50 May 18 2006 Page 1568 of 1588 REJ09B0313 0050 ...
Страница 1606: ...Appendix Rev 0 50 May 18 2006 Page 1576 of 1588 REJ09B0313 0050 ...
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