s-93a86a Seiko Instruments Inc., s-93a86a Datasheet - Page 13

• Manufacturer Part Number: s-93a86a
• Description: Cmos Serial E2prom
• Manufacturer: Seiko Instruments Inc.

Rev.2.1
Write Disable Function when Power Supply Voltage is Low
5. Write Enable (EWEN) and Write Disable (EWDS)
The S-93A86A provides a built-in detector to detect a low power supply voltage and disable writing. When
the power supply voltage is low or at power application, the write instructions (WRITE, ERASE, WRAL, and
ERAL) are cancelled, and the write disable state (EWDS) is automatically set. The detection voltage is 1.20
V typ., the release voltage is 1.35 V typ., and there is a hysteresis of about 0.15 V (Refer to Figure 10 ).
Therefore, when a write operation is performed after the power supply voltage has dropped and then risen
again up to the level at which writing is possible, a write enable instruction (EWEN) must be sent before a
write instruction (WRITE, ERASE, WRAL, or ERAL) is executed.
When the power supply voltage drops during a write operation, the data being written to an address at that
time is not guaranteed.
CS
SK
DI
The EWEN instruction is an instruction that enables a write operation. The status in which a write
operation is enabled is called the program enable mode.
The EWDS instruction is an instruction that disables a write operation. The status in which a write
operation is disabled is called the program disable mode.
After CS goes high, input an instruction in the order of the start bit, EWEN or EWDS instruction, and
address (optional). Each mode becomes valid by inputting a low level to CS after the last address
(optional) has been input.
(1) Recommendation for write operation disable instruction
It is recommended to implement a design that prevents an incorrect write operation when a write
instruction is erroneously recognized by executing the write operation disable instruction when
executing instructions other than write instruction, and immediately after power-on and before power
off.
Power supply voltage
_00
<1>
Detection voltage (−V
1.20 V Typ.
1
Figure 10 Operation when Power Supply Voltage is Low
0
2
0
3
11=EWEN
00=EWDS
Figure 9 Write Enable/Disable Timing
4
DET
5
Write instruction cancelled
Write disable state (EWDS) automatically set
Seiko Instruments Inc.
)
6
7
8Xs
Hysteresis
About 0.15 V
8
9
10
11
Release voltage (+V
1.35 V Typ.
CMOS SERIAL E
12
13
Standby
DET
S-93A86A
)
2
PROM
13