MCP7952X datasheet(33/50 Pages) MAS

33 / 50 page

 2012 Microchip Technology Inc.

Preliminary

DS22300A-page 33

MCP7952X/MCP7951X

9.1.8

DATA PROTECTION

The following protection has been implemented to pre-

vent inadvertent writes to the array:

• The write enable latch is reset on power-up

• A Write Enable instruction must be issued to set

the write enable latch

• After a byte write, page write, unique ID write, or

STATUS register write, the write enable latch is

reset

•CS must be set high after the proper number of

clock cycles to start an internal write cycle

• Access to the array during an internal EEPROM

write cycle is ignored and programming is contin-

ued

• Block protect bits are ignored for UID writes

9.1.9

CLEAR RAM INSTRUCTION

The Clear Ram instruction is a 2-byte command that

will reset the internal SRAM to the known value. Using

this command, all locations in the SRAM are set to 00h

and the data value contained in the second byte of the

command is ignored.

FIGURE 9-7:

CLRRAM

9.2

Crystal Specification and

Selection

The MCP795XX has been designed to operate with a

standard 32.768 kHz tuning fork crystal. The on-board

oscillator has been characterized to operate with a

crystal of maximum ESR of 70K Ohms.

Crystals with a comparable specification are also suit-

able for use with the MCP795XX.

The table below is given as design guidance and a

starting point for crystal and capacitor selection.

EQUATION 9-1:

The following must also be taken into consideration:

• Pin capacitance (to be included in Cx2 and Cx1)

• Stray Board Capacitance

The recommended board layout for the oscillator area

is shown in Figure 9-8. This actual board shows the

crystal and the load capacitors. In this example, C2 is

CX1, C1 is CX2 and the crystal is designated as Y1.

When calculating the effective load capacitance,

Equation 9-1 can be used.

SCK

234567

89 10 11 12 13 14 15

A7 6

1A0

Instruction

Data

High-Impedance

Manufacturer

Part Number

Crystal

Capacitance

CX1 Value

CX2 Value

Micro Crystal

CM7V-T1A

7pF

10pF

12pF

Citizen

CM200S-32.768KDZB-UT

6pF

10pF

8 pF

Please work with your crystal vendor.

Cload

CX2 CX1



CX2

CX1

-----------------------------

Cstray

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