PC87413 datasheet(144/257 Pages) NSC

144 / 257 page

8.0 Real-Time Clock (RTC) (Continued)

www.national.com

144

Revision1.2

Signal Parameters

The signal levels must conform to the voltage level requirements for 32KCLKIN/32KX1 stated in Section 11.2 on page 233.

The signal must have a duty cycle of approximately 50%. To oscillate during power-down, the signal must be sourced from

a battery-backed source. This assures that the RTC delivers updated time/calendar information.

8.2.5

Timing Generation

The timing generation function divides the 32.768 KHz clock by 215 to derive a 1 Hz signal, which serves as the input for the

seconds counter. This is performed by a divider chain composed of 15 divide-by-two latches, as shown in Figure 41.

Figure 41. Divider Chain Control

Bits 6-4 (DV2-0) of the CRA register control the following functions:

Normal operation of the divider chain (counting).

Divider chain reset to 0.

Oscillator activity when only VBAT power is present (backup state).

The divider chain can be activated by setting Normal Operation mode (bits 6-4 of CRA = 010b). The first update occurs

500 ms after divider chain activation.

Bits 3-0 of the CRA register select one the of 15 taps from the divider chain to be used as a periodic interrupt. The periodic

flag becomes active after half of the programmed period has elapsed, following divider chain activation.

See Section 8.3.13 on page 154 for more details.

8.2.6

Timekeeping

Data Format

Time is kept in BCD or binary format, as determined by bit 2 (DM) of Control Register B (CRB), and in either 12 or 24-hour

format, as determined by bit 1 of this register.

Note: When changing the above formats, re-initialize all the time registers.

Daylight Saving

Daylight saving time exceptions are handled automatically, as described in the RTC Control Register B (CRB) in Section

8.3.2 on page 150.

Leap Years

Leap year exceptions are handled automatically by the internal calendar function (every four years, February is extended to

29 days).

32.768 KHz

1Hz

Divider Chain

DV2 DV1 DV0

CRA Register

Oscillator

Enable

32KX1 /

32KX2

To other

Reset

modules

32KCLKIN

PC87413 датащи(PDF) 144 Page - National Semiconductor (TI)

PC87413 датащи(HTML) 144 Page - National Semiconductor (TI)

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 ...More

датащи скачать

ссылки URL