MCP3918 datasheet(57/88 Pages) MICROCHIP

57 / 88 page

 2014 Microchip Technology Inc.

DS20005287A-page 57

MCP3918

FIGURE 7-2:

Frame Word.

These four frames can be used to multiplex SDO at the

output of the digital isolators. In this case, up to

four channels (typically three phases and one neutral

for energy metering applications) can be multiplexed.

The output data of each individual MCP3918 device

can be attributed to a different frame (FRAME0, 1, 2 or

3), and retrieved on a single SDO line after the digital

isolators, provided that the isolators have a chip enable

or a multiplexing feature. The frame counter can then

be used to retrieve the information about which

MCP3918 part is actually being read. After the four

frames have been transmitted, the SDO pin idles logic

low to reduce digital isolator power consumption until

the next data is available. Figure 7-3 displays the

timing diagram for the 2-Wire Interface mode, showing

all OSR possibilities. Note that the first set of frames is

sent only when the first data is ready, which means that

the settling time of the sinc filter will be elapsed before

sending the first set of frames, as represented in

Figure 7-3.

FIGURE 7-3:

MCP3918 2-Wire Communication Protocol.

CRCCOM<15:0>

DATA_CH0<23:0>

SYNC WORD (2 Bytes)

SDO OUTPUT FRAME (7 Bytes, 56x clocks per Frame)

CHANNEL 0 ADC DATA (3 Bytes)

SDO

SCK/

MCLK

CRCCOM<15:0>

CRCCOM on Entire Frame (2 Bytes)

DATA_CH0<15:0>

SYNC WORD (2 Bytes)

SDO OUTPUT FRAME (6 Bytes, 48x clocks per Frame)

CHANNEL 0 ADC DATA (2 Bytes)

SDO

SCK/

MCLK

FRAME CLOCKING FOR OSR>64

FRAME CLOCKING FOR OSR=64

CRCCOM on Entire Frame (2 Bytes)

TABLE 7-4:

FRAME COUNTER SETTINGS

CNT1

CNT0

FRAME NUMBER

FRAME0

FRAME1

FRAME2

FRAME3

SDO

(OSR=64)

Internal data ready (Data is

unsettled). No frame is transmitted

Data Ready.

New data is available

OSC2/

MODE

256x

clocks

256x

clocks

256x

clocks

SCK/MCLK

256x

clocks

256x

clocks

256x

clocks

256x

clocks

256x

clocks

256x

clocks

256x

clocks

256x

clocks

256x

clocks

256x

clocks

256x

clocks

256x

clocks

256x

clocks

256x

clocks

256x

clocks

256x

clocks

256x

clocks

256x

clocks

256x

clocks

256x

clocks

256x

clocks

256x

clocks

DATA=D1

DATA=D2 DATA=D3

DATA=D4

DATA=0

DATA=D5

DATA=D6

DATA=D7

DATA=D8

DATA=D9

DATA=D10 DATA=D11 DATA=D12 DATA=D13 DATA=D14 DATA=D15 DATA=D16 DATA=D17 DATA=D18 DATA=D19 DATA=D20 DATA=D21 DATA=D22

DATA=D1

DATA=D2

DATA=D3

DATA=D4

DATA=D5

DATA=D6

DATA=D7

DATA=D8

DATA=D9

DATA=D10

DATA=D1

DATA=D2

DATA=D3

DATA=D4

DATA=D1

2-Wire Mode

Hi-Z

SDO

(OSR=128)

SDO

(OSR=256)

SDO

(OSR=512)

MCP3918 Datasheet(PDF) 57 Page - Microchip Technology

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