154 Hitachi
7.5.6
Bank Active
The synchronous DRAM has a bank active function that enables it to support high-speed accesses
of the same row address. When the RASD bit of the MCR is set to 1, the read/write command
accesses using a command without an auto precharge (READ, WRIT). In this case, even when the
access is completed, no precharge is performed. When accessing the same row address in the same
bank, a READ or WRIT command can be called immediately without calling an ACTV command,
just like the RAS down mode of the DRAM’s high-speed page mode
.
The synchronous DRAM is
divided into two banks,
so one row address in each can stay active. When the next access is to a
different row address, a PRE command is called first to precharge the bank, and access is
performed following the order of the ACTV command and READ or WRIT command after the
precharge is completed. When accesses to different row addresses follow, the precharge is
performed after the access request occurs, so the access time becomes longer. When writing,
performing an auto precharge means that no command can be called for t
RWL
+ t
AP
cycles after a
WRITA command is called. When the bank active mode is used, READ or WRIT commands can
be issued consecutively if the row address is the same. This shortens the number of cycles by
t
RWL
+ t
AP
for each write. The number of cycles between the issue of the precharge command
and the row address strobe command is determined by the TRP bit of the MCR.
Whether execution is faster when the bank active mode is used or when a basic access is used is
determined by the proportion of accesses to the same row address (P1) and the average number of
cycles from the end of one access to the next access (t
A
). When tA is longer than t
AP
, the delay
waiting for the precharge during a read becomes invisible. If t
A
is longer than t
RWL
+ t
AP
, the
delay waiting for the precharge also becomes invisible during writes. The differences between the
bank active mode and basic access speeds in these cases are the number of cycles between the start
of access and the issue of the read/write command, or (t
RP
+ t
RCD
)
×
(1 – P1) and t
RCD
.
The time that a bank can be kept active t
RAS
is limited. When it is not assured that this period will
be provided by program execution and that another row address will be accessed without a hit to
the cache, the synchronous DRAM must be set to auto refresh and the refresh cycle must be set to
the maximum value t
RAS
or less. This enables the limit on the maximum active period for each
bank to be ensured. When auto refresh is not being used, some measure must be placed in the
program to ensure that the bank does not stay active for longer than the prescribed period.
Figure 7.19 shows a burst read cycle that is not an auto precharge, figure 7.20 shows a burst read
cycle to a same row address, figure 7.21 shows a burst read cycle to different row addresses, figure
7.22 shows a write cycle without auto precharge, figure 7.23 shows a write cycle to a same row
address, and figure 7.24 shows a write cycle to different row addresses.
In figure 7.20, a cycle that does nothing, Tnop, is inserted before the Tc cycle that issues the
READ command, synchronous DRAMs, however, have a 2 cycle latency during reads for the
DQMxx signals that specify bytes. If the Tc cycle is performed immediately without inserting a
Tnop cycle, the DQMxx signal for the Td1 cycle data output cannot be specified. This is why the
Содержание SH7095
Страница 1: ...SH7095 Hardware User Manual ...
Страница 16: ...Hitachi 5 1 2 Block Diagram Figure 1 1 is a block diagram of the SH7095 Figure 1 1 Block Diagram ...
Страница 23: ...12 Hitachi ...
Страница 63: ...52 Hitachi ...
Страница 77: ...66 Hitachi ...
Страница 105: ...94 Hitachi Figure 5 14 Pipeline Operation when Interrupts are Enabled by Changing the SR ...
Страница 127: ...116 Hitachi ...
Страница 152: ...Hitachi 141 Figure 7 8 Example of 32 Bit Data Width SRAM Connection ...
Страница 157: ...146 Hitachi Figure 7 13 Synchronous DRAM 32 bit Device Connection ...
Страница 161: ...150 Hitachi Figure 7 15 Basic Burst Read Timing Auto Precharge ...
Страница 167: ...156 Hitachi Figure 7 20 Burst Read Timing Bank Active Same Row Address ...
Страница 168: ...Hitachi 157 Figure 7 21 Burst Read Timing Bank Active Different Row Addresses ...
Страница 169: ...158 Hitachi Figure 7 22 Write Timing No Precharge ...
Страница 170: ...Hitachi 159 Figure 7 23 Write Timing Bank Active Same Row Address ...
Страница 178: ...Hitachi 167 a Phase Shifted 90 by PLL b Phase Shift Using PLL is 0 Figure 7 28 Phase Shift with the PLL ...
Страница 180: ...Hitachi 169 Figure 7 29 Example of a DRAM Connection 32 Bit Data Width ...
Страница 190: ...Hitachi 179 Figure 7 36 Example of Pseudo SRAM Connection 1 M pseudo SRAM ...
Страница 191: ...180 Hitachi Figure 7 37 Example of Pseudo SRAM Connection 4 M pseudo SRAM ...
Страница 209: ...198 Hitachi Figure 7 50 Master and Partial Share Master Connections ...
Страница 218: ...Hitachi 207 EX Instruction execution MA Memory Access WB Write back Figure 8 3 Reading during a Cache Hit ...
Страница 231: ...220 Hitachi ...
Страница 287: ...276 Hitachi ...
Страница 307: ...296 Hitachi Note For a CPU writing H AA55 to FRC Figure 11 2 FRC Access Operation Write ...
Страница 308: ...Hitachi 297 Note For an FRC reading from a CPU H AA55 Figure 11 3 FRC Access Operation Read ...
Страница 333: ...322 Hitachi ...
Страница 370: ...Hitachi 359 Figure 13 12 Sample Flowchart for Receiving Multiprocessor Serial Data ...
Страница 371: ...360 Hitachi Figure 13 12 Sample Flowchart for Receiving Multiprocessor Serial Data cont ...
Страница 395: ...384 Hitachi ...
Страница 402: ...Hitachi 391 Figure 15 6 PLL Synchronization Settling Timing ...
Страница 405: ...394 Hitachi Figure 15 7 Reset Input Timing Figure 15 8 Interrupt Signal Input Timing With PLL1 Off ...
Страница 408: ...Hitachi 397 Figure 15 13 Bus Release Timing Slave Mode With PLL1 Off ...
Страница 436: ...Hitachi 425 Figure 15 33 Synchronous DRAM Mode Register Write Cycle TRP 1 Cycle ...
Страница 437: ...426 Hitachi Figure 15 34 Synchronous DRAM Mode Register Write Cycle TRP 2 Cycles ...
Страница 439: ...428 Hitachi Figure 15 36 Synchronous DRAM Auto Refresh Cycle Shown From Precharge Cycle TRP 1 Cycle TRAS 2 Cycles ...
Страница 449: ...438 Hitachi Figure 15 46 DRAM CAS Before RAS Refresh Cycle TRP 1 Cycle TRAS 2 Cycles PLL On ...
Страница 454: ...Hitachi 443 Figure 15 51 DRAM CAS Before RAS Refresh Cycle TRP 1 Cycle TRAS 2 Cycles PLL Off ...
Страница 461: ...450 Hitachi Figure 15 58 Pseudo SRAM Auto Refresh Cycle PLL On TRP 1 Cycle TRAS 2 Cycles ...
Страница 462: ...Hitachi 451 Figure 15 59 Pseudo SRAM Self Refresh Cycle PLL On TRP 1 Cycle TRAS 2 Cycles ...
Страница 467: ...456 Hitachi Figure 15 64 Pseudo SRAM Auto Refresh Cycle PLL Off TRP 1 Cycle TRAS 2 Cycles ...
Страница 468: ...Hitachi 457 Figure 15 65 Pseudo SRAM Self Refresh Cycle PLL Off TRP 1 Cycle TRAS 2 Cycles ...
Страница 471: ...460 Hitachi Figure 15 68 Interrupt Vector Fetch Cycle PLL On No Waits ...
Страница 472: ...Hitachi 461 Figure 15 69 Interrupt Vector Fetch Cycle PLL Off No Waits ...
Страница 473: ...462 Hitachi Figure 15 70 Interrupt Vector Fetch Cycle 1 External Wait Cycle ...
Страница 474: ...Hitachi 463 Figure 15 71 Address Monitor Cycle ...
Страница 490: ...Hitachi 479 B 2 Register Chart ...