D [15:0]
Data
WEOFFTIME
CSWROFFTIME = WRCYCLETIME
CSONTIME = 0
WEONTIME = 0
WRCYCLETIME
nBE0/CLE
nCS
nWE
GPMC
Figure 7-30. NAND Data Write Cycle
7.1.3.3.12.1.6 NAND Device General Chip-Select Timing Control Requirement
For most NAND devices, read data access time is dominated by CSn-to-data-valid timing and has faster
REn-to-data-valid timing. Successive accesses with CSn 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 CSn always stays low between two accesses to the same chip-select.
Moreover, an CSn deassertion time between the same chip-select NAND accesses is likely to be required
as follows: the CSn deassertion requires programming CYCLETIME and RDACCESSTIME according to
the CSn-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 CSn 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 CSn 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 REn 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.
7.1.3.3.12.1.7 Read and Write Access Size Adaptation
7.1.3.3.12.1.7.1 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.
7.1.3.3.12.1.7.2 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.
307
SPRUH73H – October 2011 – Revised April 2013
Memory Subsystem
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