X5648 INTERSIL [Intersil Corporation], X5648 Datasheet - Page 6

• Manufacturer Part Number: X5648
• Description: CPU Supervisor with 64Kbit SPI EEPROM
• Manufacturer: INTERSIL [Intersil Corporation]

Table 2. Block Protect Matrix
The Write Enable Latch (WEL) bit indicates the sta-
tus of the write enable latch. When WEL = 1, the
latch is set HIGH and when WEL = 0 the latch is reset
LOW. The WEL bit is a volatile, read only bit. It can
be set by the WREN instruction and can be reset by
the WRDS instruction.
The block lock bits, BL0 and BL1, set the level of block
lock protection. These nonvolatile bits are pro-
grammed using the WRSR instruction and allow the
user to protect one quarter, one half, all or none of the
EEPROM array. Any portion of the array that is block
lock protected can be read but not written. It will
remain protected until the BL bits are altered to disable
block lock protection of that portion of memory.
The FLAG bit shows the status of a volatile latch that
can be set and reset by the system using the SFLB
and RFLB instructions. The flag bit is automatically
reset upon power-up.
The nonvolatile WPEN bit is programmed using the
WRSR instruction. This bit works in conjunction with the
WP pin to provide an in-circuit programmable ROM func-
tion (Table 2). WP is LOW and WPEN bit programmed
HIGH disables all status register write operations.
In Circuit Programmable ROM Mode
This mechanism protects the block lock and watchdog
bits from inadvertent corruption.
In the locked state (programmable ROM Mode) the
WP pin is LOW and the nonvolatile bit WPEN is “1”.
This mode disables nonvolatile writes to the device’s
status register.
WREN CMD
Register Bits
BL1
0
0
1
1
WEL
Status
0
1
1
1
BL0
0
1
0
1
Status Register
Array Addresses Protected
WPEN
X
X
1
0
6
X5648/X5649
$1800-$1FFF
$1000-$1FFF
$0000-$1FFF
None
Device Pin
WP#
X
X
0
1
X5648, X5649
Protected Block
Protected
Protected
Protected
Protected
Block
Setting the WP pin LOW while WPEN is a “1” while an
internal write cycle to the status register is in progress
will not stop this write operation, but the operation dis-
ables subsequent write attempts to the status register.
When WP is HIGH, all functions, including nonvolatile
writes to the status register operate normally. Setting
the WPEN bit in the status register to “0” blocks the
WP pin function, allowing writes to the status register
when WP is HIGH or LOW. Setting the WPEN bit to
“1” while the WP pin is LOW activates the programma-
ble ROM mode, thus requiring a change in the WP pin
prior to subsequent status register changes. This
allows manufacturing to install the device in a system
with WP pin grounded and still be able to program the
status register. Manufacturing can then load configura-
tion data, manufacturing time and other parameters
into the EEPROM, then set the portion of memory to
be protected by setting the block lock bits, and finally
set the “OTP mode” by setting the WPEN bit. Data
changes now require a hardware change.
Read Sequence
When reading from the EEPROM memory array, CS is
first pulled low to select the device. The 8-bit READ
instruction is transmitted to the device, followed by the
16-bit address. After the READ opcode and address
are sent, the data stored in the memory at the selected
address is shifted out on the SO line. The data stored
in memory at the next address can be read sequen-
tially by continuing to provide clock pulses. The
address is automatically incremented to the next
higher address after each byte of data is shifted out.
When the highest address is reached, the address
counter rolls over to address $0000 allowing the read
cycle to be continued indefinitely. The read operation
is terminated by taking CS high. Refer to the read
EEPROM array sequence (Figure 1).
To read the status register, the CS line is first pulled low
to select the device followed by the 8-bit RDSR instruc-
tion. After the RDSR opcode is sent, the contents of the
status register are shifted out on the SO line. Refer to
the read status register sequence (Figure 2).
Unprotected Block
Protected
Writable
Writable
Writable
Block
WPEN, BL0, BL1
Status Register
WD0, WD1
Protected
Protected
Writable
Writable
March 17, 2005
FN8136.0