The Watchdog Timer bits, WD0 and WD1, select the
Watchdog Time-out Period. These nonvolatile bits are
programmed with the WRSR instruction.
Status Register Bits
0 1 600 Milliseconds
1 0 200 Milliseconds
7036 FRM T05
The read only 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 Programmable Hardware Write Protec-
tion (Table 2). When WP is LOW and the WPEN bit is pro-
grammed HIGH, all Status Register Write Operations are
In Circuit Programmable ROM Mode
This mechanism protects the Block Lock and Watchdog
bits from inadvertant corruption. It may be used to per-
form an In Circuit Programmable ROM function by hard-
wiring the WP pin to ground, writing and Block Locking
the desired portion of the array to be ROM, and then pro-
gramming the WPEN bit HIGH.
When reading from the E2PROM 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 sequentially by
continuing to provide clock pulses. The address is auto-
matically 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 E2PROM 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).
Prior to any attempt to write data into the device, the
“Write Enable” Latch (WEL) must ﬁrst be set by issuing
the WREN instruction (Figure 3). CS is ﬁrst taken LOW,
then the WREN instruction is clocked into the device.
After all eight bits of the instruction are transmitted, CS
must then be taken HIGH. If the user continues the Write
Operation without taking CS HIGH after issuing the
WREN instruction, the Write Operation will be ignored.
To write data to the E2PROM memory array, the user then
issues the WRITE instruction followed by the 16 bit
address and then the data to be written. Any unused
address bits are speciﬁed to be “0’s”. The WRITE opera-
tion minimally takes 32 clocks. CS must go low and
remain low for the duration of the operation. If the address
counter reaches the end of a page and the clock contin-
ues, the counter will roll back to the ﬁrst address of the
page and overwrite any data that may have been previ-
Table 2. Block Protect Matrix
WPEN, BL0, BL1
WD0, WD1, BITS
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