S-93C76A Datasheet, PDF (12/33 Pages) Seiko Instruments Inc – CMOS SERIAL E2PROM

CMOS SERIAL E²PROM
S-93C76A
Rev.3.2_00
3. Write enable (EWEN) and write disable (EWDS)
The EWEN instruction is used to enable a write operation. The status in which a write operation is
enabled is called the program-enabled mode.
The EWDS instruction is used to disable a write operation. The status in which a write operation is
disabled is called the program-disabled mode.
The write operation is disabled upon power application and detection of a low supply voltage. To
prevent an unexpected write operation due to external noise or a CPU malfunctions, it should be kept in
write disable mode except when performing write operations, after power-on and before shutdown.
CS
SK
1 2 3 4 5 6 7 8 9 10 11 12 13
DI
<1> 0 0
8Xs
11 = EWEN
00 = EWDS
Figure 11 Write Enable/Disable Timing
Stand by
„ Start Bit
A start bit is recognized by latching the high level of DI at the rising edge of SK after changing CS to high
(start bit recognition). A write operation begins by inputting the write instruction and setting CS to low.
Subsequently, by setting CS to high again, the DO pin outputs a low level if the write operation is still in
progress and a high level if the write operation is complete (verify operation). Therefore, only after a write
operation, in order to input the next command, CS is set to high, which switches the DO pin from a high-
impedance state (Hi-Z) to a data output state. However, if start bit is recognized, the DO pin returns to the
high-impedance state (refer to Figure 5 Timing Chart).
Make sure that data output from the CPU does not interfere with the data output from the serial memory IC
when configuring a 3 -wire interface by connecting the DI input pin and DO output pin, as such interference
may cause a start bit fetch problem. Take the measures described in “„ 3-Wire Interface (Direct
Connection between DI and DO)”.
12
Seiko Instruments Inc.