Datasheet

© 2009 Microchip Technology Inc. DS22153C-page 37
MCP9843/98243
5.3.3 WRITE PROTECTION
The MCP98243 has a Software Write-Protect (SWP)
feature that allows the lower half array (addresses
00h -7Fh) to be write-protected or permanently write-
protected (PWP). The write protected area can be
cleared by sending Clear Write Protect (CWP)
command. However, once the PWP is executed the
protected memory can not be cleared. The device will
not respond to the CWP command.
To access write protection, the device address code of
the Address Byte is set to ‘0110’ instead of ‘1010’. The
‘1010’ Address code is used to access the memory
area and the ‘0110’ address code is used to access the
write protection. Once the device is write protected it
will not acknowledge certain commands. Table 5-3
shows the corresponding Address Bytes for the write
protect feature.
TABLE 5-3: WRITE PROTECT DEVICE ADDRESSING (NOTE 1)
EEPROM Operation
Address Pins Address Byte
A2 A1 A0 Address Code
Slave Address
R/W
A2 A1 A0
SWP WRITE GND GND V
HV
0110 0 0 1 0
READ 1
CWP WRITE GND V
DD
V
HV
0110 0 1 1 0
READ 1
PWP (Note) WRITE X X X 0110 XX X 0
READ 1
Note 1: The Address Pins are ‘X’ or don’t cares. However, the slave address bits need to match the address pins.
For V
HV
voltage levels, refer to Figure 2-13.
TABLE 5-4: DEVICE RESPONSE WHEN WRITING DATA OR ACCESSING SWP/CWP/PWP
(NOTE 1)
Status Command ACK Address ACK Data Byte ACK Write Cycle
Not
Protected
SWP/CWP/PWP ACK X ACK X ACK Yes
Page/byte write ACK Address ACK Data ACK Yes
Protected
with
SWP
SWP NoACK X NoACK X NoACK No
CWP ACK X ACK X ACK Yes
PWP ACK X ACK X ACK Yes
Page/byte write lower 128 bytes ACK Address ACK Data NoACK No
Permanently
Protected
SWP/CWP/PWP NoACK X NoACK X NoACK No
Page/byte write lower 128 bytes ACK Address ACK Data NoACK No
Note 1: X is defined as ‘don’t care’.