MCP7940NT-ESLASHMS datasheet(31/58 Pages) MICROCHIP

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DS20005010J-page 31

MCP7940N

5.6.2

COARSE TRIM MODE

When CRSTRIM = 1, Coarse Trim mode is enabled.

While in this mode, the MCP7940N will apply trimming

at a rate of 128 Hz. If SQWEN is set, the MFP will out-

put a trimmed 64 Hz nominal clock signal.

Because trimming is applied at a rate of 128 Hz rather

than

once

every

minute,

each

step

the

TRIMVAL<6:0> value has a significantly larger effect

on the resulting time deviation and output clock

frequency.

By monitoring the MFP output frequency while in this

mode, the user can easily observe the TRIMVAL<6:0>

value affecting the clock timing.

TABLE 5-12:

SUMMARY OF REGISTERS ASSOCIATED WITH DIGITAL TRIMMING

Note 1: The 64 Hz Coarse Trim mode square

wave output is not available while operat-

ing from the backup power supply.

2: With Coarse Trim mode enabled, the

TRIMVAL<6:0> value has a drastic effect

on timing. Leaving the mode enabled

during normal operation will likely result

in inaccurate time.

Name

Bit 7

Bit 6

Bit 5

Bit 4

Bit 3

Bit 2

Bit 1

Bit 0

on Page

CONTROL

OUT

SQWEN

ALM1EN

ALM0EN

EXTOSC

CRSTRIM

SQWFS1

SQWFS0

OSCTRIM

SIGN

TRIMVAL6 TRIMVAL5 TRIMVAL4

TRIMVAL3

TRIMVAL2 TRIMVAL1 TRIMVAL0

Legend:

— = unimplemented location, read as ‘0’. Shaded cells are not used by digital trimming.

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