MCP3304 datasheet(22/40 Pages) MICROCHIP

22 / 40 page

MCP3302/04

DS21697B-page 22

 2002 Microchip Technology Inc.

7.0

SERIAL COMMUNICATIONS

7.1

Output Code Format

The output code format is a binary two’s complement

scheme, with a leading sign bit that indicates the sign

of the output. If the IN+ input is higher than the IN-

input, the sign bit will be a zero. If the IN- input is higher,

the sign bit will be a ‘1’.

The diagram shown in Figure 7-1 shows the output

code transfer function. In this diagram, the horizontal

axis is the analog input voltage and the vertical axis is

the output code of the ADC. It shows that when IN+ is

equal to IN-, both the sign bit and the data word is zero.

As IN+ gets larger with respect to IN-, the sign bit is a

zero and the data word gets larger. The full scale output

code is reached at +4095 when the input [(IN+) - (IN-)]

reaches VREF - 1 LSB. When IN- is larger than IN+, the

two’s complement output codes will be seen with the

sign bit being a one. Some examples of analog input

levels and corresponding output codes are shown in

Table 7-1.

TABLE 7-1:

BINARY TWO’S

COMPLEMENT OUTPUT

CODE EXAMPLES.

FIGURE 7-1:

Output Code Transfer Function.

Analog Input Levels

Sign

Bit

Binary Data

Decimal

DATA

Full Scale Positive

(IN+)-(IN-)=VREF-1 LSB

1111 1111 1111

+4095

(IN+)-(IN-) = VREF-2 LSB

1111 1111 1110

+4094

IN+ = (IN-) +2 LSB

0000 0000 0010

IN+ = (IN-) +1 LSB

0000 0000 0001

IN+ = IN-

0000 0000 0000

IN+ = (IN-) - 1 LSB

1111 1111 1111

-1

IN+ = (IN-) - 2 LSB

1111 1111 1110

-2

(IN+)-(IN-) = VREF-2 LSB

0000 0000 0001

-4095

Full Scale Negative

(IN+)-(IN-) = VREF-1 LSB

0000 0000 0000

-4096

IN+ > IN-

IN+ < IN-

0 + 0000 0000 0001 (+1)

0 + 0000 0000 0010 (+2)

0 + 0000 0000 0011 (+3)

1 + 1111 1111 1101 (-3)

1 + 1111 1111 1110 (-2)

1 + 1111 1111 1111 (-1)

0 + 1111 1111 1110 (+4094)

0 + 1111 1111 1111 (+4095)

1 + 0000 0000 0000 (-4096)

1 + 0000 0000 0001 (-4095)

Output

Code

0 + 0000 0000 0000 (0)

VREF

-VREF

Positive Full

Scale Output = VREF -1 LSB

Negative Full

Scale Output = -VREF

Analog Input

IN+ - IN-

Voltage

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