Datasheet

 2010-2014 Microchip Technology Inc. DS20005010F-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 of 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
Register
on Page
CONTROL
OUT SQWEN ALM1EN ALM0EN EXTOSC CRSTRIM SQWFS1 SQWFS0 26
OSCTRIM SIGN TRIMVAL6 TRIMVAL5 TRIMVAL4 TRIMVAL3 TRIMVAL2 TRIMVAL1 TRIMVAL0 29
Legend: — = unimplemented location, read as ‘0’. Shaded cells are not used by digital trimming.