X76F640 Datasheet, PDF (7/17 Pages) Xicor Inc. – Secure SerialFlash

X76F640
Figure 5. Acknowledge Polling
SCL
8th clk.
of 8th
pwd. byte
‘ACK’
clk
8th
‘ACK’
clk
clk
SDA
‘ACK’
START
condition
8th bit
ACK or
no ACK
7025 FM 10
READ OPERATIONS
Read operations are initiated in the same manner as write
operations but with a different command code.
Random Read
The master issues the start condition and a Read instruction
and password, performs a Password Ack Polling, then
issues the word address. Once the password has been
acknowledged and first byte has been read, another start
can be issued followed by a new 8-bit address. Random
reads are allowed, but only the low order 8 bits can
change. This limits random reads to a 256 byte block.
Therefore, with a single password cycle only a 256 byte
block of array 0 may be accessed randomly. To randomly
access another block of array 0, a stop must be issued fol-
lowed by a new command/address/password sequence. A
random read of the array 1 can access all locations with-
out another password command sequence.
Figure 6. Random Read
SDA _S
COMMAND
Read
Password
7
Sequential Read
The host can read sequentially within an array after the
password acceptance sequence. The data output is
sequential, with the data from address n followed by the
data from n+1. The address counter for read operations
increments all address bits, allowing the entire memory
array contents to be serially read during one operation. At
the end of the address space (address 1FFFh for array 0, 1Fh
for array 1), the counter “rolls o
ver” to address 0 and
the X76F640 continues to output data for each acknowl- edge
received. Refer to figure 7 for the address, acknowl-
edge and data transfer sequence. An acknowledge must
follow each 8-bit data transfer. After the last bit has been
read, a stop condition is generated without a preceding
acknowledge.
Read
Password
0
Wait tWC OR
Repeated
ACK Polling
Command
If ACK, then
Password Matches
ACK POLLING
COMMAND
S
S
Data X
S
Data Y
7025 FM 11
7