X76F641
Figure 5. Acknowledge Polling
SCL
8th clk.
of 8th
pwd. byte
‘ACK’
clk
8th
clk
‘ACK’
clk
SDA
‘ACK’
START
condition
8th bit
ACK or
no ACK
7025 FM 10
READ OPERATIONS
Sequential Read
Read operations are initiated in the same manner as write The host can read sequentially within an array after the
password acceptance sequence. The data output is
operations but with a different command code.
sequential, with the data from address n followed by the data
from n+1. The address counter for read operations
Random Read
The master issues the start condition and a Read instruc- increments all address bits, allowing the entire memory
tion and password, performs a Password Ack Polling, then array contents to be serially read during one operation. At
issues the word address. Once the password has been the end of the address space (address 1FFFh for array 0,
acknowledged and first byte has been read, another start 1Fh for array 1), the counter “rolls over” to address 0 and the
X76F641 continues to output data for each acknowl- edge
can be issued followed by a new 8-bit address. Random
reads are allowed, but only the low order 8 bits can received. Refer to figure 7 for the address, acknowledge
change. This limits random reads to a 256 byte block. edge and data transfer sequence. An acknowledge must
follow each 8-bit data transfer. After the last bit has been
Therefore, with a single password cycle only a 256 byte
block of array 0 may be accessed randomly. To randomly read, a stop condition is generated without a preceding
access another block of array 0, a stop must be issued fol- acknowledge.
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
START
Read
Password
7
Read
Password
0
COMMAND
SDA S
ACK
ACK
ACK
ACK
START
Wait t
WC
OR
Repeated
ACK Polling
Command
If ACK, then
Password Matches
START
A15
A14
A13
A12
A11
A10
STOP
S
ACK
Data Y
7025 FM 11
ACK POLLING
COMMAND
A9
A8
A7
A6
A5
A4
A3
A2
A1
A0
S
ACK
ACK
NACK
ACK
Data X
S
7
A7
A6
A5
A4
A3
A2
A1
A0
ICMIC [ IC MICROSYSTEMS ]
