MCP7940NT datasheet(9/36 Pages) MICROCHIP

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 2011 Microchip Technology Inc.

DS25010A-page 9

MCP7940N

4.0

RTCC FUNCTIONALITY

The MCP7940N family is a highly integrated RTCC.

On-board time and date counters are driven from a low-

power oscillator to maintain the time and date. An

integrated VCC switch enables the device to maintain

the time and date and also the contents of the SRAM

during a VCC power failure.

4.1

RTCC MEMORY MAP

The RTCC registers are contained in addresses

0x00h-0x1fh. 64 bytes of user-accessable SRAM are

located in the address range 0x20-0x5f. The SRAM

memory is a separate block from the RTCC control

and Configuration registers. All SRAM locations are

battery-backed-up during a VCC power fail. Unused

locations are not accessible, MCP7940N will noACK

after the address byte if the address is out of range.

The shaded areas are not implemented and read as

‘0’. No error checking is provided when loading time

and date registers.

• Addresses 0x00h-0x06h are the RTCC Time and

Date registers. These are read/write registers.

Care must be taken when accessing these regis-

ters while the oscillator is running.

• Incorrect data can appear in the Time and Date

registers if a write is attempted during the time

frame where these internal registers are being

incremented. The user can minimize the likeli-

hood of data corruption by ensuring that any

writes to the Time and Date registers occur before

the contents of the second register reach a value

of 0x59H.

• Addresses 0x07h-0x09h are the device Configu-

ration and Calibration.

• Addresses 0x0Ah-0x10h are the Alarm 0 regis-

ters. These are used to set up the Alarm 0, the

Interrupt polarity and the Alarm 0 compare.

• Addresses 0x11h-0x17h are the same as 0x0Bh-

0x11h but are used for Alarm 1.

• Addresses 0x18h-0x1Fh are used for the time-

stamp feature.

The Memory Map is shown in Table 4-1.

TABLE 4-1:

RTCC MEMORY MAP

Address

Bit 7

Bit 6

Bit 5

Bit 4

Bit 3

Bit 2

Bit 1

Bit 0

Function

Range

Reset

State

00h

10 Seconds

Seconds

00-59

00h

01h

10 Minutes

Minutes

00-59

00h

02h

12/24

10 Hour

AM/PM

10 Hour

Hour

Hours

1-12 + AM/PM

00 - 23

00h

03h

OSCON

VBAT

VBATEN

Day

1-7

01h

04h

10 Date

Date

01-31

01h

05h

10 Month

Month

01-12

01h

06h

10 Year

Year

00-99

01h

07h

OUT

SQWE

ALM1

ALM0

EXTOSC

RS2

RS1

RS0

Control Reg.

80h

08h

CALIBRATION

Calibration

00h

09h

RESERVED – DO NOT USE

00h

0Ah

10 Seconds

Seconds

00-59

00h

0Bh

10 Minutes

Minutes

00 - 59

00h

0Ch

12/24

10 Hour

AM/PM

10 Hours

Hour

Hours

1-12 + AM/PM

00-23

00h

0Dh

ALM0POL

ALM0C2

ALM0C1

ALM0C0

ALM0IF

Day

1-7

01h

0Eh

10 Date

Date

01-31

01h

0Fh

10 Month

Month

01-12

01h

10h

Reserved – Do not use

Reserved

01h

11h

10 Seconds

Seconds

00-59

00h

12h

10 Minutes

Minutes

00-59

00h

13h

12/24

10 Hour

AM/PM

10 Hours

Hour

Hours

1-12 + AM/PM

00-23

00h

14h

ALM1POL

ALM1C2

ALM1C1

ALM1C0

ALM1IF

Day

1-7

01h

15h

10 Date

Date

01-31

01h

16h

10 Month

Month

01-12

01h

17h

Reserved – Do not use

Reserved

01h

18h

10 Minutes

Minutes

00h

19h

12/24

10 Hour

AM/PM

10 Hours

Hour

00h

1Ah

10 Date

Date

00h

1Bh

Day

10 Month

Month

00h

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