© 2008 Microchip Technology Inc.

DS21034E-page 17

MCP3202

5.0

SERIAL COMMUNICATIONS

5.1

Overview

Communication with the MCP3202 is done using a

standard SPI-compatible serial interface. Initiating

communication with the 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

bit. The SGL/DIFF bit and the ODD/SIGN bit follow the

start bit and are used to select the input channel

configuration. The SGL/DIFF is used to select single

ended or psuedo-differential mode. The ODD/SIGN bit

selects which channel is used in single ended mode,

and is used to determine polarity in pseudo-differential

mode. Following the ODD/SIGN bit, the MSBF bit is

transmitted to and is used to enable the LSB first format

for the device. If the MSBF bit is high, then the data will

come from the device in MSB first format and any

further clocks with CS low will cause the device to

output zeros. If the MSBF bit is low, then the device will

output the converted word LSB first after the word

has been transmitted in the MSB first format.

See Figure 5-2. Table 5-1 shows the configuration bits

for the MCP3202. The device will begin to sample the

analog input on the second rising edge of the clock,

after the start bit has been received. The sample period

will end on the falling edge of the third clock following

the start bit.

On the falling edge of the clock for the MSBF bit, the

device will output a low null bit. The next sequential

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,

(and MSBF = 1), 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

often done when dealing with microcontroller-based

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

Section 6.1 “Using the MCP3202 with Microcon-

troller (MCU) SPI Ports”

for more details on using the

MCP3202 devices with hardware SPI ports.

FIGURE 5-1:

Communication with the MCP3202 using MSB first format only.

TABLE 5-1:

CONFIGURATION BITS FOR

THE MCP3202

Config

Bits

Channel

Selection

GND

SGL/

DIFF

ODD/

SIGN

01

Single Ended

Mode

10

+

—

-

11

—

+

-

Pseudo-

Differential

Mode

00

IN+

IN-

01

IN-

IN+

CS

CLK

MS

HI-Z

Null

Bit B11 B10 B9 B8 B7 B6 B5 B4 B3 B2 B1 B0*

HI-Z

SGL/

DIFF

Start

* After completing the data transfer, if further clocks are applied with CS low, the A/D Converter will output zeros

indefinitely. See Figure 5-2 below for details on obtaining LSB first data.

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

ODD/

SIGN BF

Don’t Care

SGL/

DIFF

Start

ODD/

SIGN