© 2007 Microchip Technology Inc.

DS21700C-page 21

MCP3301

7.2

Communicating with the MCP3301

Communication with the device is completed using a

standard SPI compatible serial interface. Initiating com-

munication with the MCP3301 begins with the CS

going low. If the device was powered up with the CS pin

low, it must be brought high and back low to initiate

communication. The device will begin to sample the

analog input on the first rising edge of CLK after CS

goes low. The sample period will end in the falling edge

of the second clock, at which time 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. 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 pro-

vided to the device while CS is still low (after the LSB

first data has been transmitted), the device will clock

out zeros indefinitely.

FIGURE 7-2:

Communication with MCP3301 (MSB first Format).

FIGURE 7-3:

Communication with MCP3301 (LSB first Format).

CS

CLK

D

OUT

Power

Down

t

SUCS

t

CONV

t

* After completing the data transfer, if further clocks are applied with CS low, the ADC will output LSB first data,

followed by zeros indefinitely. See Figure 7-2 below.

** t

high impedance node, leaving the CLK running to clock out the LSB-first data or zeros.

t

CSH

NULL

BIT

B11 B10 B9

B8

B7

B6

B5

B4

B3

B2

B1

HI-Z

HI-Z

NULL

BIT

SB B11 B10 B9

SB

CS

CLK

D

OUT

Power Down

t

SUCS

t

CONV

t

* After completing the data transfer, if further clocks are applied with CS low, the ADC will output zeros indefi-

nitely.

** t

high impedance node, leaving the CLK running to clock out the LSB-first data or zeros.

t

CSH

NULL

BIT

B11

B10

B9

B8

B7

B6

B5

B4

B3

B2

B1

B0

HI-Z

B1

B2

B3

B4

B5

B6

B7

B8

B9

B10

SB

*

HI-Z

SB

B11