X46402 Datasheet, PDF (12/23 Pages) Xicor Inc. – Dual Voltage CPU Supervisor with 64K Password Protected EEPROM

X46402
Figure 12. Acknowledge Polling
Preliminary Information
SCL
8th clk.
of 8th
pwd. byte
‘ACK’
clk
8th
‘ACK’
clk
clk
SDA
‘ACK’
START
condition
8th bit
ACK or
no ACK
PASSWORD PROTECTED READ OPERATIONS
Password protected read operations are initiated in the
same manner as password protected write operations but
with a different command code.
Password Random Read (Data Array, OTP Arrays)
Data from a password protected array can be randomly
read after sending a single password. To do this, the mas-
ter issues a start bit, sends a Password Read instruction
and read password, performs Password Ack Polling, then
issues the desired 2 byte address. The host receives the
first byte from the X46402 and sends a NACK, followed
by a repeated start bit. A new 8-bit address specifies the
next byte to read. This process can continue indefinitely
as long as the each byte read out of the X46402 is
“NACKed” and followed by a repeated start.
The address automatically increments after each read
operation. As such, a special case arises. A random read
of address 00FFh automatically increments to 0100h
after reading the byte. Consider the following example.
Example: A system needs data from password protected
locations 0020h and 0150h and the designer does not
wish to send the password twice. After receiving data
from 0020h, the host sends a NACK and a repeated
start, followed by address byte FFh. The data read from
location 0FFh is ignored, but the operation has adjusted
the address pointer to 100h. Another NACK and repeated
start followed by the address 50h allows the contents of
150h to be read by the host.
A random read of either of the OTP arrays can access all
locations of both arrays without another password com-
mand sequence.
A password random read operation will also return valid
data if accessing a non-password protected area of the
array. See Figure 13.
Password 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 the
memory array, 7Fh for the OTP array) the device goes
into an idle state and data output is all “1s”. To continue
reading at another address requires a new Read opera-
tion. Refer to Figure 14 for the address, acknowledge and
data transfer sequence. An acknowledge must follow
each 8-bit data transfer. After the last bit has been read,
the host sends a stop condition with or without a preced-
ing acknowledge.
After sending a Password Read command and the cor-
rect password, the entire array, including non-password
protected areas will be read with a sequential read com-
mand.
After sending a Password Array Read command and cor-
rect password, the entire array, including non-password
protected areas are read by a sequential read command.
NON-PASSWORD READ OPERATIONS
Non-password protected read operations are initiated in
the same manner as non-password protected write oper-
ations but with a different command code.
No-Password Random Read
The master issues the start condition, then a No-password
Read instruction, then issues the word address. Once the
first byte has been read, another start can be issued fol-
lowed by a new 8-bit address. A No-Password random
read operation is not allowed to a password protected
area. In a No-Password Random Read from address
00FFh, the address pointer changes to 100h after output-
ting the data byte and operates in the same manner as the
password protected operation. See Figure 15.
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