MCP7940N-ESLASHMS datasheet(15/58 Pages) MICROCHIP

15 / 58 page

 2011-2022 Microchip Technology Inc. and its subsidiares

DS20005010J-page 15

MCP7940N

5.3

Timekeeping

The MCP7940N maintains the current time and date

using an external 32.768 kHz crystal or clock source.

Separate registers are used for tracking seconds, min-

utes, hours, day of week, date, month, and year. The

MCP7940N automatically adjusts for months with less

than 31 days and compensates for leap years from

2001 to 2399. The year is stored as a two-digit value.

Both 12-hour and 24-hour time formats are supported

and are selected using the 12/24 bit.

The day of week value counts from 1 to 7, increments

at midnight, and the representation is user-defined (i.e.,

the MCP7940N does not require 1 to equal Sunday,

etc.).

All time and date values are stored in the registers as

binary-coded decimal (BCD) values. The MCP7940N

will continue to maintain the time and date while oper-

ating off the backup supply.

When reading from the timekeeping registers, the reg-

isters are buffered to prevent errors due to rollover of

counters. The following events cause the buffers to be

updated:

• When a read is initiated from the RTCC registers

(addresses 0x00 to 0x1F)

• During an RTCC register read operation, when

the register address rolls over from 0x1F to 0x00

The timekeeping registers should be read in a single

operation to utilize the on-board buffers and avoid

rollover issues.

5.3.1

DIGIT CARRY RULES

The following list explains which timer values cause a

digit carry when there is a rollover:

• Time of day: from 11:59:59 PM to 12:00:00 AM

(12-hour mode) or 23:59:59 to 00:00:00 (24-hour

mode), with a carry to the Date and Weekday

fields

• Date: carries to the Month field according to Table

5-3

• Weekday: from 7 to 1 with no carry

• Month: from 12/31 to 01/01 with a carry to the

Year field

• Year: from 99 to 00 with no carry

TABLE 5-3:

DAY TO MONTH ROLLOVER

SCHEDULE

Note 1: Loading invalid values into the time and

date registers will result in undefined

operation.

2: To avoid rollover issues when loading

new time and date values, the oscilla-

tor/clock input should be disabled by

clearing the ST bit for External Crystal

mode and the EXTOSC bit for External

Clock Input mode. After waiting for the

OSCRUN bit to clear, the new values can

be loaded and the ST or EXTOSC bit can

then be re-enabled.

Month

Name

Maximum Date

January

February

28 or 29(1)

March

April

May

June

July

August

September

October

November

December

Note 1: 29 during leap years, otherwise 28.

MCP7940N-E/MS Datasheet(PDF) 15 Page - Microchip Technology

MCP7940N-E/MS Datasheet(HTML) 15 Page - Microchip Technology

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

Datasheet Download

Link URL