7
FN8131.3
December 9, 2015
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The watchdog timer bits, WD0 and WD1, select the
watchdog time out period. These nonvolatile bits are
programmed with the WRSR instruction.
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. This flag can be used by the system to determine
whether a reset occurs as a result of a watchdog time out or
power failure.
Note: The Watch Dog Timer is shipped disabled. (WD1 = 1,
WD0 = 1. The factory default for Memory Block Protection is
‘None’. (BL1 = 0, BL0 = 0).
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 function (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.
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 disables
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 programmable 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
configuration 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 sequentially by continuing to provide
clock pulses. The address is automatically incremented to
the next higher address after each byte of data is shifted out.
STATUS
REGISTER BITS ARRAY ADDRESSES PROTECTED
BL1 BL0 X5323/X5325
0 0 None (factory default)
0 1 $0C00 to $0FFF
1 0 $0800 to $0FFF
1 1 $0000 to $0FFF
STATUS REGISTER BITS
WATCHDOG TIME-OUT
(TYPICAL)WD1 WD0
0 0 1.4s
0 1 600ms
1 0 200ms
1 1 disabled (factory default)
0 1 2 3 4 5 6 7 8 9 10 20 21 22 23 24 25 26 27 28 29 30
7 6543210
DATA OUT
CS
SCK
SI
SO
MSB
HIGH IMPEDANCE
INSTRUCTION
16-BIT ADDRESS
15 14 13 3 2 1 0
FIGURE 5. READ EEPROM ARRAY SEQUENCE
X5323, X5325