MCP3918 datasheet(53/88 Pages) MICROCHIP

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 2014 Microchip Technology Inc.

DS20005287A-page 53

MCP3918

6.12

Interface Mode Selection

(SPI or 2-Wire)

The MCP3918 includes two different digital interfaces:

a standard 4-wire half duplex SPI interface (see

Section 6.0 “SPI Serial Interface Description”

) and

a 2-wire interface dedicated for digitally isolated

applications (see Section 7.0 “2-Wire Serial Interface

Description”

The selection between these two interfaces is possible

only when the CLKEXT bit is high (CLKEXT = 1). This

is the case by default at POR. When the CLKEXT = 1

condition is true, the OSC2/MODE pin becomes the

selection input pin for the Interface mode.

When

OSC2/MODE

logic

low

during

the

CLKEXT = 1 condition, the SPI interface is selected.

When OSC2/MODE pin is logic high, the 2-Wire

Interface is selected (see Figure 1-5 for the 2-Wire

mode selection timing diagram).

If OSC2/MODE pin is left floating while CLKEXT = 1,

internal

pull-down

(35 µA

typical

current)

automatically selects the SPI mode as the default

interface.

The MODE selection is not combinatorial, it is latched

at each POR, Hard Reset and Watchdog Time Reset.

In other words, to change from one interface mode to

another, the user needs to create one of these three

resets and change the OSC2/MODE logic input state

before exiting the applied reset.

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