MCP7940N-ESLASHMS datasheet(27/58 Pages) MICROCHIP

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DS20005010J-page 27

MCP7940N

5.5.1

SQUARE WAVE OUTPUT MODE

The MCP7940N can be configured to generate a

square wave clock signal on MFP. The input clock

frequency, FOSC, is divided according to the

SQWFS<1:0> bits as shown in Table 5-8.

The square wave output is not available when operat-

ing from the backup power supply.

TABLE 5-8:

CLOCK OUTPUT RATES

5.5.2

ALARM INTERRUPT OUTPUT

MODE

The MFP will provide an interrupt output when enabled

alarms match and the square wave clock output is dis-

abled. This prevents the user from having to poll the

alarm interrupt flag to check for a match.

The alarm interrupt output is available when operating

from the backup power supply.

The ALMxIF flags control when the MFP is asserted, as

described in the following sections.

5.5.2.1

Single Alarm Operation

When only one alarm module is enabled, the MFP output

is based on the corresponding ALMxIF flag and the

ALMPOL flag. If ALMPOL = 1, the MFP output reflects

the value of the ALMxIF flag. If ALMPOL = 0, the MFP

output reflects the inverse of the ALMxIF flag (Table 5-9).

TABLE 5-9:

SINGLE ALARM OUTPUT

TRUTH TABLE

5.5.2.2

Dual Alarm Operation

When both alarm modules are enabled, the MFP out-

put is determined by a combination of the ALM0IF,

ALM1IF, and ALMPOL flags.

If ALMPOL = 1, the ALM0IF and ALM1IF flags are

OR’d together and the result is output on MFP. If

ALMPOL = 0, the ALM0IF and ALM1IF flags are AND’d

together, and the result is inverted and output on MFP

(Table 5-10). This provides the user with flexible

options for combining alarms.

TABLE 5-10:

DUAL ALARM OUTPUT

TRUTH TABLE

5.5.3

GENERAL PURPOSE OUTPUT

MODE

If the square wave clock output and both alarm mod-

ules are disabled, the MFP acts as a general purpose

output. The output logic level is controlled by the OUT

bit.

The general purpose output is not available when

operating from the backup power supply.

Note:

All of the clock output rates are affected by

digital trimming except for the 1:1

postscaler value (SQWFS<1:0> = 11).

SQWFS<1:0>

Postscaler

Nominal

Frequency

1:32,768

1 Hz

1:8

4.096 kHz

1:4

8.192 kHz

1:1

32.768 kHz

Note 1: Nominal frequency assumes FOSC is

32.768 kHz.

ALMPOL

ALMxIF(1)

MFP

001

010

100

111

Note 1: ALMxIF refers to the interrupt flag corre-

sponding to the alarm module that is

enabled.

Note:

If ALMPOL = 0 and both alarms are

enabled, the MFP will only assert when

both ALM0IF and ALM1IF are set.

ALMPOL

ALM0IF

ALM1IF

MFP

0001

0011

0101

0110

1000

1011

1101

1111

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