FOR AUTOMOTIVE 105

°C OPERATION 3-WIRE SERIAL E

S-93C76A H Series

Seiko Instruments Inc.

13

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.

<1>

2

3

4

5

6

7

8

9

10

11

12

13

DI

SK

CS

11 = EWEN

00 = EWDS

Standby

1

8Xs

0

0

Figure 11 Write Enable/Disable Timing



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 (High-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)”.