M41T315Y datasheet(13/24 Pages) STMICROELECTRONICS

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M41T315Y*, M41T315V, M41T315W

CLOCK OPERATION

Clock Register Information

Clock information is contained in eight registers of

8 bits, each of which is sequentially accessed 1 bit

at a time after the 64-bit pattern recognition se-

quence has been completed. When updating the

clock registers, each must be handled in groups of

8 bits. Writing and reading individual bits within a

READ/WRITE registers are defined in Table

5., page 13.

Data contained in the clock registers is in binary

coded decimal format (BCD). Reading and writing

the registers is always accomplished by stepping

though all eight registers, starting with Bit 0 of

AM-PM/12/24 Mode

Bit 7 of the hours register is defined as the 12-hour

or 24-hour mode select bit. When high, the 12-

hour mode is selected. In the 12-hour mode, Bit 5

is the AM/PM bit with logic high being PM. In the

24-hour mode, Bit 5 is the second 10-hour bit (20-

23 hours).

Oscillator and Reset Bits

Bits 4 and 5 of the day register are used to control

the reset and oscillator functions. Bit 4 controls the

reset pin input. When the Reset Bit is set to logic

'1,' the reset input pin is ignored. When the Reset

Bit is set to logic '0,' a low input on the reset pin will

cause the device to abort data transfer without

changing data in the timekeeping registers. Reset

operates independently of all other inputs. Bit 5

controls the oscillator. When set to logic '0,' the os-

cillator turns on and the real time clock/calendar

begins to increment.

Zero Bits

Registers 1, 2, 3, 4, 5, and 6 contain one (1) or

more bits that will always read logic '0.' When writ-

ing to these locations, either a logic '1' or '0' is ac-

ceptable.

Table 5. RTC Register Map

Keys:

A/P = AM/PM Bit

12/24 = 12 or 24-hour mode Bit

OSC = Oscillator Bit

RST = Reset Bit

0 = Must be set to '0'

Figure 11. Reset Pulse Waveform

Function/Range

BCD Format

0.1 Seconds

0.01 Seconds

Seconds

00-99

10 Seconds

Seconds

00-59

10 Minutes

Minutes

00-59

312/24

10 /

A/P

Hrs

Hours (24 Hour Format)

Hours

01-12/

00-23

OSC

RST

Day of the Week

Day

01-7

10 date

Date: Day of the Month

Date

01-31

10M

Month

01-12

10 Years

Year

00-99

tRST

RST

AI04260

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