2-WIRE CMOS SERIAL E2PROM
S-24CS01A/02A/04A/08A
Rev.4.4_00
3. Matching phases while E2PROM is accessed
The S-24CS01A/02A/04A/08A 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 26 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.
Start
condition
Stop
condition
Start
condition
Dummy clock
1
2
8
9
SCL
SDA
Figure 26 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.
22
Seiko Instruments Inc.
SII [ SEIKO INSTRUMENTS INC ]
