MCP3551-ESLASHMS datasheet(25/36 Pages) MICROCHIP

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DS21950E-page 25

MCP3550/1/3

5.5

Using The MCP3550/1/3 with

Microcontroller (MCU) SPI Ports

It is required that the microcontroller SPI port be

configured to clock out data on the falling edge of clock

and latch data in on the rising edge. Figure 5-6 depicts

the operation shown in SPI mode 1,1, which requires

that the SCK from the MCU idles in the High state,

while Figure 5-7 shows the similar case of SPI Mode

0,0, where the clock idles in the Low state. The

waveforms in the figures are examples of an MCU

operating the SPI port in 8-bit mode, and the

MCP3550/1/3 devices do not require data in 8-bit

groups.

In SPI mode 1,1, data is read using only 24 clocks or

three byte transfers. The data ready bit must be read

by testing the SDO/RDY line prior to a falling edge of

the clock.

In SPI mode 0,0, data is read using 25 clocks or four

byte transfers. Please note that the data ready bit is

included in the transfer as the first bit in this mode.

FIGURE 5-6:

SPI Communication – Mode 1,1.

FIGURE 5-7:

SPI Communication – Mode 0,0.

SCK

SDO/RDY

MCU

Data stored into MCU

receive

after

transmission of first byte

Receive

Buffer

Data

stored

into

MCU

receive

after

transmission of second byte

Data stored into MCU

receive

after

transmission of third byte

DO O 21 20 19 18 17

15 14 13 12 11 10 9

76 5 4 3 2 1

OL OH 21 20 19 18 17 16

15 14 13 12 11 10 9

3 2

RH L

SCK

SDO/RDY

MCU

Data stored into MCU

receive

after

transmission of first byte

Receive

Buffer

Data

stored

into

MCU

receive

after

transmission of second byte

Data stored into MCU

receive

after

transmission of third byte

Data stored into MCU

receive

after

transmission of fourth byte

DR OO 21 20 19 18 17

14 13 12 11 10 9

65 4 3 2

OH OL 21 20 19 18 17

15 14 13 12 11 10 9

3 2

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