MCP7952X/MCP7951X
9.1.2
MULTIFUNCTION PIN (MFP)
TABLE 9-1:
Supply
VBAT CHANGOVER
CONDITIONS
Pin 9 is a multifunction pin and supports the following
functions:
Read/Write Powered
• The value of the OUT bit determines the logic.
Condition
Access
By
• Level of the I/O. This is only available when
operating from VCC.
VCC < VTRIP, VCC < VBAT
VCC > VTRIP, VCC < VBAT
VCC > VTRIP, VCC > VBAT
No
Yes
Yes
VBAT
VCC
VCC
• Alarm Outputs – Available in VBAT mode
• FOUT mode – Driven from a FOSC divider – Not
available in VBAT mode.
For more information on VBAT conditions see the RTCC
Best Practices Application Note, AN1365 (DS01365).
The internal control logic for the MFP is connected to
the switched internal supply bus. This allows operation
in VBAT mode. The Alarm Output is the only mode that
operates in VBAT mode, other modes are suspended.
9.1.4
UNIQUE ID LOCATIONS
When the unique ID locations are preprogrammed from
the factory with either an EUI-48 or EUI-64, the EUI
code is programmed into location 0x00-0x07. Loca-
tions 0x08-0x0F are blank (0x0F).
9.1.3
VBAT SWITCHOVER
If the VBAT feature is not used, the VBAT pin should be
connected to GND. A low value series resistor and
Schottky diode are recommended between the
external battery and the VBAT pin to reduce inrush
current and also to prevent any leakage current
reaching the external VBAT source.
Note:
For EUI-64, the data is located in address
0x00-0x07. For EUI-48 locations, 0x02-
0x07 contain the data. 0x00/01 contain
0xFF.
The VTRIP point is defined as 1.5V typical. When VDD
falls below 1.5V the system will continue to operate
the RTCC and SRAM using the VBAT supply. There is
~50mV hyst in the trip point changeover. The following
conditions apply:
To read the unique ID location the IDREAD command
is given with the starting address. Valid addresses are
0x00 through 0x0F. All 16 bytes can be read out in a
single command by clocking the device. Trying to
access locations past 0x0F will result in the address
wrapping within these 16 bytes.
FIGURE 9-2:
IDREAD COMMAND SEQUENCE
CS
0
1
2
3
4
5
6
7
8
9 10 11 12 13 14 15 16 17 18 19 20 21 22 23
SCK
SI
Instruction
Address Byte
0
0
1
1
0
0
1
1
0
0
0
0
3
2
1
0
Don’t Care
Data Out
High-Impedance
7
6
5
4
3
2
1
0
SO
Address range is 0x00-0x0F, address counter will wrap within this range.
To write to the unique ID locations, the IDWRITE com-
mand is used. The device must be write enabled and
the correct unlock sequence must have been per-
formed. See Section 10.1.4, Write to the Unlock
Register for more details.
The ID locations can be written to using the IDWRITE
command. The valid address is between 0x00 and
0x0F. The entire 16 bytes must be written in two
groups of 8 bytes. A maximum of 8 bytes can be
written at once.
DS22300A-page 28
Preliminary
2012 Microchip Technology Inc.
MAS [ MICRO ANALOG SYSTEMS ]
