R2025S/D
Data Transmission under Special Condition
The R2025S/D holds the clock tentatively for duration from Start Condition to avoid invalid read or write clock on
carrying clock. When clock carried during this period, which will be adjusted within approx. 61µs from Stop
Condition. To prevent invalid read or write, clock and calendar data 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 R2025S/D is automatically released to release tentative hold of the clock, and access from the CPU
is forced to be terminated (The same action as made Stop Condition is received: automatic resume function from
I2C-Bus interface). Therefore, one access must be complete within 0.5 seconds. The automatic resume
function prevents delay in clock even if SCL is stopped from sudden failure of the system during clock read
operation.
Also a second Start Condition after the first Start Condition and before the Stop Condition is regarded “Repeated
Start Condition”. Therefore, when 0.5 to 1.0 seconds passed after the first Start Condition, an access to the
R2025S/D 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.
The user shall always be able to access the real-time clock as long as three conditions are met.
(1) No Stop Condition shall be generated until clock and calendar data read/write is started and completed.
(2) One cycle read/write operation shall be complete 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.
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 read the read as 05:59:59. Then the R2025S/D confirms (Stop
Condition) and carries second digit being hold and the time change 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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RICOH [ RICOH ELECTRONICS DEVICES DIVISION ]
