MCP3204/3208

DS21298B-page 14

Preliminary

© 1999 Microchip Technology Inc.

5.0

SERIAL COMMUNICATIONS

Communication with the MCP3204/3208 devices is

done 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 D

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 config-

uration bits for the MCP3204 and MCP3208, respec-

tively. 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 (D

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 D

often done when dealing with microcontroller-based

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

Section 6.1

for

more

details

on

using

the

MCP3204/3208 devices with hardware SPI ports.

CONTROL BIT

SELECTIONS

INPUT

CONFIGURATION

CHANNEL

SELECTION

SINGLE/

DIFF

D2*

D1

D0

1

X

0

0

single ended

CH0

1

X

0

1

single ended

CH1

1

X

1

0

single ended

CH2

1

X

1

1

single ended

CH3

0

X

0

0

differential

CH0 = IN+

CH1 = IN-

0

X

0

1

differential

CH0 = IN-

CH1 = IN+

0

X

1

0

differential

CH2 = IN+

CH3 = IN-

0

X

1

1

differential

CH2 = IN-

CH3 = IN+

*D2 is don’t care for MCP3204

TABLE 5-1:

Configuration Bits for the MCP3204.

CONTROL BIT

SELECTIONS

INPUT

CONFIGURATION

CHANNEL

SELECTION

SINGLE/

DIFF

D2

D1

D0

1

0

0

0

single ended

CH0

1

0

0

1

single ended

CH1

1

0

1

0

single ended

CH2

1

0

1

1

single ended

CH3

1

1

0

0

single ended

CH4

1

1

0

1

single ended

CH5

1

1

1

0

single ended

CH6

1

1

1

1

single ended

CH7

0

0

0

0

differential

CH0 = IN+

CH1 = IN-

0

0

0

1

differential

CH0 = IN-

CH1 = IN+

0

0

1

0

differential

CH2 = IN+

CH3 = IN-

0

0

1

1

differential

CH2 = IN-

CH3 = IN+

0

1

0

0

differential

CH4 = IN+

CH5 = IN-

0

1

0

1

differential

CH4 = IN-

CH5 = IN+

0

1

1

0

differential

CH6 = IN+

CH7 = IN-

0

1

1

1

differential

CH6 = IN-

CH7 = IN+

TABLE 5-2:

Configuration Bits for the MCP3208.