Datasheet

 2012-2018 Microchip Technology Inc. DS20002300C-page 15
MCP7951X/MCP7952X
FIGURE 5-4: SUGGESTED PLACEMENT OF THE OSCILLATOR CIRCUIT
5.2.2 EXTERNAL CLOCK INPUT
A 32.768 kHz external clock source can be connected
to the X1 pin (Figure 5-5). When using this
configuration, the X2 pin should be left floating.
FIGURE 5-5: EXTERNAL CLOCK INPUT
OPERATION
5.2.3 OSCILLATOR FAILURE STATUS
The MCP795XX features an oscillator failure flag,
OSCRUN, that indicates whether or not the oscillator is
running. The OSCRUN bit is automatically set after 32
oscillator cycles are detected. If no oscillator cycles are
detected for more than T
OSF, then the OSCRUN bit is
automatically cleared (Figure 5-6). This can occur if the
oscillator is stopped by clearing the ST bit or due to
oscillator failure.
FIGURE 5-6: OSCILLATOR FAILURE STATUS TIMING DIAGRAM
TABLE 5-2: SUMMARY OF REGISTERS ASSOCIATED WITH OSCILLATOR CONFIGURATION
GND
`
X1
X2
DEVICE PINS
CX1
CX2
GND
X1
X2
Bottom Layer
Copper Pour
Oscillator
Crystal
Top Layer Copper Pour
CX1
CX2
DEVICE PINS
(tied to ground)
(tied to ground)
Single-Sided and In-line Layouts: Fine-Pitch (Dual-Sided) Layouts:
Oscillator
Crystal
Copper Pour
(tied to ground)
Note: The EXTOSC bit must be set to enable an
external clock source.
X1
Clock from
Ext. Source
MCP795XX
Name Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0
Register
on Page
RTCSEC
ST
SECTEN2 SECTEN1 SECTEN0 SECONE3 SECONE2 SECONE1 SECONE0 17
RTCWKDAY
— — OSCRUN PWRFAIL VBATEN WKDAY2 WKDAY1 WKDAY0
19
CONTROL
— SQWEN ALM1EN ALM0EN EXTOSC CRSTRIM SQWFS1 SQWFS0 28
Legend: — = unimplemented location, read as ‘0’. Shaded cells are not used by oscillator configuration.
X1
OSCRUN Bit
< TOSF
TOSF
32 Clock Cycles