MCP3304 datasheet(23/40 Pages) MICROCHIP

23 / 40 page

 2002 Microchip Technology Inc.

DS21697B-page 23

MCP3302/04

7.2

Communicating with the MCP3302

and MCP3304

Communication with the MCP3302/04 devices is done

using a standard SPI-compatible serial interface. Initi-

ating communication with either device is done by

bringing the CS line low (see Figure 7-2). 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. Each channel in

single ended mode will operate as a 12-bit converter

with a unipolar output. No negative codes will be output

in single ended mode. The next three bits (D0, D1 and

D2) are used to select the input channel configuration.

Table 7-2 and Table 7-3 show the configuration bits for

the MCP3302 and MCP3304, 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.

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

complete the sample and hold period (DIN 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 13

clocks will output the result of the conversion with the

sign bit first, followed by the 12 remaining data bits, as

shown in Figure 7-2. Note that if the device is operating

in the single ended mode, the sign bit will always be

transmitted as a ‘0’. Data is always output from the

device on the falling edge of the clock. If all 13 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 7-3. 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 7.3 for more details on using the MCP3302/04

devices with hardware SPI ports

TABLE 7-2:

CONFIGURATION BITS FOR

THE MCP3302

TABLE 7-3:

CONFIGURATION BITS FOR

THE MCP3304

Control Bit

Selections

Input

Configuration

Channel

Selection

Single

/Diff

D2* D1 D0

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 don’t care for MCP3302

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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