MCP3204 datasheet(19/40 Pages) MICROCHIP

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DS21298E-page 19

MCP3204/3208

5.0

SERIAL COMMUNICATIONS

Communication with the MCP3204/3208 devices is

accomplished using a standard SPI-compatible serial

interface. Initiating communication with either device is

done by bringing the CS line low (see Figure 5-1). If the

device was powered up with the CS pin low, it must be

brought high and back low to initiate communication.

The first clock received with CS low and DIN high will

constitute a start bit. The SGL/DIFF bit follows the start

bit and will determine if the conversion will be done

using single-ended or differential input mode. The next

three bits (D0, D1 and D2) are used to select the input

channel configuration. Table 5-1 and Table 5-2 show

the configuration bits for the MCP3204 and MCP3208,

respectively. The device will begin to sample the

analog input on the fourth rising edge of the clock after

the start bit has been received. The sample period will

end on the falling edge of the fifth clock following the

start bit.

Once the D0 bit is input, one more clock is required to

complete the sample and hold period (D

IN is a “don’t

care” for this clock). On the falling edge of the next

clock, the device will output a low null bit. The next 12

clocks will output the result of the conversion with MSB

first, as shown in Figure 5-1. Data is always output from

the device on the falling edge of the clock. If all 12 data

bits have been transmitted and the device continues to

receive clocks while the CS is held low, the device will

output the conversion result LSB first, as shown in

Figure 5-2. If more clocks are provided to the device

while CS is still low (after the LSB first data has been

transmitted), the device will clock out zeros indefinitely.

If necessary, it is possible to bring CS low and clock in

leading zeros on the DIN line before the start bit. This is

often done when dealing with microcontroller-based

SPI ports that must send 8 bits at a time. Refer to

Section 6.1 “Using the MCP3204/3208 with Micro-

controller (MCU) SPI Ports”

for more details on using

the MCP3204/3208 devices with hardware SPI ports.

TABLE 5-1:

CONFIGURATION BITS FOR

THE MCP3204

TABLE 5-2:

CONFIGURATION BITS FOR

THE MCP3208

Control Bit

Selections

Input

Configuration

Channel

Selection

Single/

Diff

D2* D1

single-ended

CH0

single-ended

CH1

single-ended

CH2

single-ended

CH3

differential

CH0 = IN+

CH1 = IN-

differential

CH0 = IN-

CH1 = IN+

differential

CH2 = IN+

CH3 = IN-

differential

CH2 = IN-

CH3 = IN+

D2 is a “don’t care” for MCP3204

Control Bit

Selections

Input

Configuration

Channel

Selection

Single

/Diff

D1 D0

single-ended

CH0

single-ended

CH1

single-ended

CH2

single-ended

CH3

single-ended

CH4

single-ended

CH5

single-ended

CH6

single-ended

CH7

differential

CH0 = IN+

CH1 = IN-

differential

CH0 = IN-

CH1 = IN+

differential

CH2 = IN+

CH3 = IN-

differential

CH2 = IN-

CH3 = IN+

differential

CH4 = IN+

CH5 = IN-

differential

CH4 = IN-

CH5 = IN+

differential

CH6 = IN+

CH7 = IN-

differential

CH6 = IN-

CH7 = IN+

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