D [15:0]
Data
WEOFFTIME
CSWROFFTIME = WRCYCLETIME
CSONTIME = 0
WEONTIME = 0
WRCYCLETIME
nBE0/CLE
nCS
nWE
Preliminary
Architecture
www.ti.com
Figure 5-30. NAND Data Write Cycle
5.2.4.12.1.6 NAND Device General Chip-Select Timing Control Requirement
For most NAND devices, read data access time is dominated by CS-to-data-valid timing and has faster
RE-to-data-valid timing. Successive accesses with CS deassertions between accesses are affected by
this timing constraint. Because accesses to a NAND device can be interleaved with other chip-select
accesses, there is no certainty that CS always stays low between two accesses to the same
chip-select. Moreover, an CS deassertion time between the same chip-select NAND accesses is likely
to be required as follows: the CS deassertion requires programming CYCLETIME and
RDACCESSTIME according to the CS-to-data-valid critical timing.
To get full performance from NAND read and write accesses, the prefetch engine can dynamically
reduce RDCYCLETIME, WRCYCLETIME, RDACCESSTIME, WRACCESSTIME, CSRDOFFTIME,
CSWROFFTIME, ADVRDOFFTIME, ADVWROFFTIME, OEOFFTIME, and WEOFFTIME on
back-to-back NAND accesses (to the same memory) and suppress the minimum CS high pulse width
between accesses. For more information about optimal prefetch engine access, see
.
Some NAND devices require minimum write-to-read idle time, especially for device-status read
accesses following status-read command programming (write access). If such write-to-read transactions
are used, a minimum CS high pulse width must be set. For this, CYCLE2CYCLESAMECSEN and
CYCLE2CYCLEDELAY must be set according to the appropriate timing requirement to prevent any
timing violation.
NAND devices usually have an important RE high to data bus in tristate mode. This requires a bus
turnaround setting (BUSTURNAROUND = 1), so that the next access to a different chip-select is
delayed until the BUSTURNAROUND delay completes. Back-to-back NAND read accesses to the
same NAND Flash are not affected by the programmed bus turnaround delay.
5.2.4.12.1.7 Read and Write Access Size Adaptation
5.2.4.12.1.7.1 8-Bit Wide NAND Device
Host 16-bit word and 32-bit word read and write access requests to a chip-select associated with an
8-bit wide NAND device are split into successive read and write byte accesses to the NAND memory
device. Byte access is ordered according to little-endian organization. A NAND 8-bit wide device must
be interfaced on the D0D7 interface bus lane. GPMC data accesses are justified on this bus lane when
the chip-select is associated with an 8-bit wide NAND device.
5.2.4.12.1.7.2 16-Bit Wide NAND Device
Host 32-bit word read and write access requests to a chip-select associated with a 16-bit wide NAND
device are split into successive read and write 16-bit word accesses to the NAND memory device.
16-bit word access is ordered according to little-endian organization.
606
General-Purpose Memory Controller (GPMC)
SPRUGX9 – 15 April 2011
© 2011, Texas Instruments Incorporated
Содержание TMS320C6A816 Series
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