CY14B101I Ver la hoja de datos (PDF) - Cypress Semiconductor
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CY14B101I Datasheet PDF : 42 Pages
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PRELIMINARY
CY14C101I
CY14B101I, CY14E101I
Real Time Clock Operation
nvTIME Operation
The CY14X101I offers internal registers that contain clock,
alarm, watchdog, interrupt, and control functions. The RTC
registers occupy a separate address space from nvSRAM and
are accessible through the Read RTC register and Write RTC
register sequence on register addresses 0x00 to 0x0F. Internal
double buffering of the clock and the timer information registers
prevents accessing transitional internal clock data during a read
or write operation. Double buffering also circumvents disrupting
normal timing counts or the clock accuracy of the internal clock
when accessing clock data. Clock and alarm registers store data
in BCD format.
Clock Operations
The clock registers maintain time up to 9,999 years in
one-second increments. The time can be set to any calendar
time and the clock automatically keeps track of days of the week
and month, leap years, and century transitions. There are eight
registers dedicated to the clock functions, which are used to set
time with a write cycle and to read time during a read cycle.
These registers contain the time of day in BCD format. Bits
defined as ‘0’ are currently not used and are reserved for future
use by Cypress.
Reading the Clock
The double buffered RTC register structure reduces the chance
of reading incorrect data from the clock. Stop internal updates to
the CY14X101I time keeping registers before reading clock data
to prevent reading of data in transition. Stopping the register
updates does not affect clock accuracy.
When an read sequence of RTC device is initiated, the update
of the user timekeeping registers stops and does not restart until
a STOP or a Repeated START condition is generated. The RTC
registers are read while the internal clock continues to run. After
the end of read sequence, all the RTC registers are
simultaneously updated within 20 ms.
Setting the Clock
A write access to the RTC device stops updates to the time
keeping registers and enables the time to be set. The correct
day, date, and time is then written into the registers and must be
in 24 hour BCD format. The time written is referred to as the
“Base Time”. This value is stored in nonvolatile registers and
used in the calculation of the current time. When a STOP or a
Repeated START condition is encountered, the values of
timekeeping registers are transferred to the actual clock
counters after which the clock resumes normal operation. If a
valid STOP or Repeated START condition is not generated by
the master, the time written to the RTC registers is never trans-
ferred to the actual clock counters.
If the time written to the timekeeping registers is not in the correct
BCD format, each invalid nibble of the RTC registers continue
counting to 0xF before rolling over to 0x0 after which RTC
resumes normal operation.
Note After ‘W’ bit is set to ‘0’, values written into the timekeeping,
alarm, calibration, and interrupt registers are transferred to the
RTC time keeping counters in tRTCp time. These counter values
must be saved to nonvolatile memory either by initiating a
Software/Hardware STORE or AutoStore operation. While
working in AutoStore disabled mode, perform a STORE
operation after tRTCp time while writing into the RTC registers for
the modifications to be correctly recorded.
Backup Power
The RTC in the CY14X101I is intended for permanently powered
operation. The VRTCcap or VRTCbat pin is connected depending
on whether a capacitor or battery is chosen for the application.
When the primary power, VCC, fails and drops below VSWITCH
the device switches to the backup power supply.
The clock oscillator uses very little current, which maximizes the
backup time available from the backup source. Regardless of the
clock operation with the primary source removed, the data stored
in the nvSRAM is secure, having been stored in the nonvolatile
elements when power was lost.
During backup operation, the CY14X101I consumes a 0.45 µA
(Typ) at room temperature. The user must choose capacitor or
battery values according to the application.
Backup time values based on maximum current specifications
are shown in the following table. Nominal backup times are
approximately two times longer.
Table 8. RTC Backup Time
Capacitor Value
0.1F
0.47F
1.0F
Backup Time
(CY14B101I)
60 hours
12 days
25 days
Using a capacitor has the obvious advantage of recharging the
backup source each time the system is powered up. If a battery
backup is used, a 3-V lithium battery is recommended and the
CY14X101I sources current only from the battery when the
primary power is removed. However, the battery is not recharged
at any time by the CY14X101I. The battery capacity must be
chosen for total anticipated cumulative down time required over
the life of the system.
Stopping and Starting the Oscillator
The OSCEN bit in the calibration register at 0x08 controls the
enable and disable of the oscillator. This bit is nonvolatile and is
shipped to customers in the “enabled” (set to ‘0’) state. To
preserve the battery life when the system is in storage, OSCEN
must be set to ‘1’. This turns off the oscillator circuit, extending
the battery life. If the OSCEN bit goes from disabled to enabled,
it takes approximately one second (two seconds maximum) for
the oscillator to start.
While system power is off, if the voltage on the backup supply
(VRTCcap or VRTCbat) falls below their respective minimum level,
the oscillator may fail.The CY14X101I has the ability to detect
oscillator failure when system power is restored. This is recorded
in the Oscillator Fail Flag (OSCF) of the flags register at the
address 0x00. When the device is powered on (VCC goes above
VSWITCH) the OSCEN bit is checked for the ‘enabled’ status. If
the OSCEN bit is enabled and the oscillator is not active within
the first 5 ms, the OSCF bit is set to ‘1’. The system must check
for this condition and then write ‘0’ to clear the flag.
Note that in addition to setting the OSCF flag bit, the time
registers are reset to the ‘Base Time’ (when a read sequence of
the RTC device is initiated, the update of the user timekeeping
Document #: 001-54391 Rev. *C
Page 21 of 42
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