D A T A S H E E T
tions” and “Programmable Wait State” for further
38-3Fh, and the burst sequence would be
39-3A-3B-3C-3D-3E-3F-38h. The burst sequence
begins with the starting address written to the device,
but wraps back to the first address in the selected
group. In a similar fashion, the 16-word and 32-word
Linear Wrap modes begin their burst sequence on the
starting address written to the device, and then wrap
back to the first address in the selected address group.
Note that in these three burst read modes the
address pointer does not cross the boundary that
occurs every 64 words; thus, no wait states are
inserted (except during the initial access).
details).
The initial word is output t
the first CLK cycle. Subsequent words are output t
after the rising edge of
IACC
BACC
after the rising edge of each successive clock cycle,
which automatically increments the internal address
counter. Note that the device has a fixed internal
address boundary that occurs every 64 words,
starting at address 00003Eh. The transition from
the highest address 3FFFFFh to 000000h is also a
boundary crossing. During the time the device is out-
putting the 64th word (address 00003Eh, 00007Eh,
0000BEh, etc.), a two cycle latency occurs before data
appears for the next address (address 00003Fh,
00007Fh, 0000BFh, etc.). The RDY output indicates
this condition to the system by pulsing low. See Figure
19.
If the clock frequency is less than 6 MHz during a burst
mode operation, additional latencies will occur. RDY
indicates the length of the latency by pulsing low.
Programmable Wait State
The programmable wait state feature indicates to the
device the number of additional clock cycles that must
elapse after AVD# is driven active before data will be
available. Upon power up, the device defaults to the
maximum of seven total cycles. The total number of
wait states is programmable from two to seven cycles.
The device will continue to output continuous, sequen-
tial burst data, wrapping around to address 000000h
after it reaches the highest addressable memory loca-
tion, until the system asserts CE# high, RESET# low,
or AVD# low in conjunction with a new address. See
Table 1. The reset command does not terminate the
burst read operation.
The wait state command sequence requires three
cycles; after the two unlock cycles, the third cycle
address should be written according to the desired wait
state as shown in Table 8. Address bits A11-A0 should
be set to 555h, while addresses bits A16-A12 set the
wait state. For further details, see “Set Configuration
Register Command Sequence”.
If the host system crosses the bank boundary while
reading in burst mode, and the device is not program-
ming or erasing, a two-cycle latency will occur as
described above. If the host system crosses the bank
boundary while the device is programming or erasing,
the device will provide asynchronous read status infor-
mation. The clock will be ignored. After the host has
completed status reads, or the device has completed
the program or erase operation, the host can restart a
burst operation using a new address and AVD# pulse.
Handshaking Feature
The handshaking feature allows the host system to
simply monitor the RDY signal from the device to deter-
mine when the initial word of burst data is ready to be
read. The host system should use the wait state
command sequence to set the number of wait states
for optimal burst mode operation (02h for 40 MHz
clock, 03h for 54 and 66 MHz clock). The initial word of
burst data is indicated by the rising edge of RDY after
OE# goes low.
If the clock frequency is less than 6 MHz during a burst
mode operation, additional latencies will occur. RDY
indicates the length of the latency by pulsing low.
8-, 16-, and 32-Word Linear Burst with Wrap Around
The remaining three modes are of the linear wrap
around design, in which a fixed number of words are
read from consecutive addresses. In each of these
modes, the burst addresses read are determined by
the group within which the starting address falls. The
groups are sized according to the number of words
read in a single burst sequence for a given mode (see
Table 2.)
The handshaking feature may be verified by writing the
autoselect command sequence to the device. See
“Autoselect Command Sequence” for details.
For optimal burst mode performance on devices
without the handshaking option, the host system must
set the appropriate number of wait states in the flash
device depending on such factors as clock frequency,
presence of a boundary crossing, or an odd or even
starting address. See “Set Configuration Register
Command Sequence” section for more information.
Table 2. Burst Address Groups
Mode
8-word
16-word
32-word
Group Size Group Address Ranges
8 words
16 words
32 words
0-7h, 8-Fh, 10-17h, 18-1Fh...
0-Fh, 10-1Fh, 20-2Fh, 30-3Fh...
00-1Fh, 20-3Fh, 40-5Fh, 60-7Fh...
The autoselect function allows the host system to dis-
tinguish flash devices that have handshaking from
those that do not. See the “Autoselect Command
Sequence” section for more information.
As an example: if the starting address in the 8-word
mode is 39h, the address range to be read would be
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Am29BDS643G
25692A2 May 8, 2006
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