S-24C02BPPHL Datasheet, PDF (21/39 Pages) Seiko Instruments Inc – 2-WIRE CMOS SERIAL E2PROM

Rev.2.2_00
2-WIRE CMOS SERIAL E²PROM
S-24C02BPPHL
4. Maximum effectiveness of write protection
The following conditions must be satisfied to prevent erroneous writing at power-on due to write protection.
(1) Set the WP pin to high level at a time other than when the write instruction is being executed, including
during power-on or off.
(2) Adjust the phase after power-on.
Pulling up the WP pin to V_CC to always enable the WP pin at the absolute maximum rated voltage or lower
prohibits writing all the time regardless of the conditions of the VCC, SDA, and SCL pins.
5. Matching phases while E²PROM is accessed
The S-24C02BPPHL does not have a pin for resetting (the internal circuit), therefore, the E²PROM cannot
be forcibly reset externally. If a communication interruption occurs in the E²PROM, it must be reset by
software.
For example, even if a reset signal is input to the microprocessor, the internal circuit of the E²PROM is not
reset as long as the stop condition is not input to the E²PROM. In other words, the E²PROM retains the
same status and cannot shift to the next operation. This symptom applies to the case when only the
microprocessor is reset when the power supply voltage drops. With this status, if the power supply voltage
is restored, reset the E²PROM (after matching the phase with the microprocessor) and input an instruction.
The following shows this reset method.
[How to reset E²PROM]
The E²PROM can be reset by the start and stop instructions. When the E²PROM is reading data “0” or
is outputting the acknowledge signal, 0 is output to the SDA line. In this status, the microprocessor
cannot output an instruction to the SDA line. In this case, terminate the acknowledge output operation
or read operation, and then input a start instruction. Figure 22 shows this procedure.
First, input the start condition. Then transmit 9 clocks (dummy clocks) of SCL. During this time, the
microprocessor sets the SDA line to high level. By this operation, the E²PROM interrupts the
acknowledge output operation or data output, so input the start condition^*1. When a start condition is
input, the E²PROM is reset. To make doubly sure, input the stop condition to the E²PROM. Normal
operation is then possible.
SCL
SDA
Start
condition
Dummy clock
1
2
8
9
Start
condition
Stop
condition
Figure 22 Resetting E²PROM
*1. After 9 clocks (dummy clocks), if the SCL clock continues to be output without a start condition
being input, a write operation may be started upon receipt of a stop condition. To prevent this, input
a start condition after 9 clocks (dummy clocks).
Remark It is recommended to perform the above reset using dummy clocks when the system is
initialized after the power supply voltage has been raised.
Seiko Instruments Inc.
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