RV5C387A_03 datasheet(30/49 Pages) RICOH

Part #	RV5C387A

Description	I2C bus SERIAL INTERFACE REAL-TIME CLOCK IC WITH VOLTAGE MONITORING FUNCTION

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Manufacturer	RICOH [RICOH electronics devices division]

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RV5C387A

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1.2-6 Data transmission under special condition

The RV5C387A holds the clock tentatively for duration from start condition to stop condition to avoid invalid read or

write clock on carrying clock. When clock is carried during this period, which will be adjusted within approx. 61µs

from stop condition. To prevent invalid read or write clock shall be made during one transmission operation (from

start condition to stop condition). When 0.5 to 1.0 second elapses after start condition any access to the RV5C387A

is automatically released to release tentative hold of the clock, set Fh to the address pointer, and access from the

CPU is forced to be terminated (the same action as made stop condition is received: automatic resume function from

the I

2C bus interface). Therefore, one access must be completed within 0.5 seconds. The automatic resume

function prevents delay in clock even if the SCL is stopped from sudden failure of the system during clock read

operation.

Also a second start condition after the first condition and before the stop condition is regarded as the “repeated start

condition.” Therefore, when 0.5 to 1.0 seconds passed after the first start condition, access to the RV5C387A is

automatically released.

If access is tried after automatic resume function is activated, no acknowledge signal will be output for writing while

FFh will be output for reading.

Access to the Real-time Clock

1) No stop condition shall be generated until clock read/write is started and completed.

2) One cycle read/write operation shall be completed within 0.5 seconds.

3) Do not make Start Condition within 61µs from Stop Condition. When clock is carried during the access,

which will be adjusted within approx. 61µs from Stop Condition.

The user shall always be able to access the real-time clock as long as these three conditions are met.

Bad example of reading from seconds to hours (invalid read)

(Start condition)

→ (Read of seconds) → (Read of minutes) → (Stop condition) → (Start condition) → (Read

of hour)

→ (Stop condition)

Assuming read was started at 05:59:59 P.M. and while reading seconds and minutes the time advanced to

06:00:00 P.M. At this time second digit is hold so the read as 05:59:59. Then the RV5C387A confirms (Stop

condition) and carries second digit being hold and the time changes to 06:00:00 P.M. Then, when the hour

digit is read, it changes to 6. The wrong results of 06:59:59 will be read.

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RV5C387A Datasheet(PDF) 30 Page - RICOH electronics devices division

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