MCP795W21 datasheet(31/54 Pages) MAS

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 2011 Microchip Technology Inc.

Preliminary

DS22280A-page 31

MCP795WXX/MCP795BXX

The debounce will only operate if the clock is running

and these timings are based on the uncalibrated

32.768 kHz clock.

• EVHS<1:0> – These bits determine how many

high-speed events must occur before the EVHIF

bit is set. All of these events must occur within

250 ms.

- 00 – 1st Event

- 01 – 4th Event

- 10 – 16th Event

- 11 – 32nd Event

9.1.5

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.

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:

For more information on VBAT conditions see the RTCC

Best Practices Application Note, AN1365 (DS01365).

9.1.6

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).

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

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

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.

TABLE 9-1:

VBAT CHANGOVER

CONDITIONS

Supply

Condition

Read/Write

Access

Powered

VCC < VTRIP, VCC < VBAT

VBAT

VCC > VTRIP, VCC < VBAT

Yes

VCC

VCC > VTRIP, VCC > VBAT

Yes

VCC

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.

SCK

23456789 10 11 12 13 14 15 16 17 18 19 20 21 22

76543210

Instruction

Address Byte

Data Out

High-Impedance

Don’t Care

Address range is 0x00-0x0F, address counter will wrap within this range.

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