LTC1286CS8 datasheet(12/24 Pages) LINER

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LTC1286/LTC1298

Start Bit

The first “logical one” clocked into the DIN input after CS

goes low is the start bit. The start bit initiates the data

transfer. The LTC1298 will ignore all leading zeros which

precede this logical one. After the start bit is received, the

remaining bits of the input word will be clocked in. Further

inputs on the DIN pin are then ignored until the next CS

cycle.

Multiplexer (MUX) Address

The bits of the input word following the START bit assign

the MUX configuration for the requested conversion. For

a given channel selection, the converter will measure the

voltage between the two channels indicated by the + and

– signs in the selected row of the following tables. In

single-ended mode, all input channels are measured with

respect to GND.

APPLICATION INFORMATION

Input Data Word

The LTC1286 requires no DIN word. It is permanently

configured to have a single differential input. The conver-

sion result appears on the DOUT line. The data format is

MSB first followed by the LSB sequence. This provides

easy interface to MSB or LSB first serial ports. For MSB

first data the CS signal can be taken high after B0 (see

Figure 1). The LTC1298 clocks data into the DIN input on

the rising edge of the clock. The input data words are

defined as follows:

MSBF bit is a logical zero, LSB first data will follow the

normal MSB first data on the DOUT line. (see Operating

Sequence)

Transfer Curve

The LTC1286/LTC1298 are permanently configured for

unipolar only. The input span and code assignment for

this conversion type are shown in the following figures.

MSB First/LSB First (MSBF)

The output data of the LTC1298 is programmed for

MSB first or LSB first sequence using the MSBF bit.

When the MSBF bit is a logical one, data will appear on

the DOUT line in MSB first format. Logical zeros will be

filled in indefinitely following the last data bit. When the

Operation with DIN and DOUT Tied Together

The LTC1298 can be operated with DIN and DOUT tied

together. This eliminates one of the lines required to

communicate to the microprocessor (MPU). Data is trans-

mitted in both directions on a single wire. The processor

pin connected to this data line should be configurable as

either an input or an output. The LTC1298 will take control

of the data line and drive it low on the 4th falling CLK edge

after the start bit is received (see Figure 3). Therefore the

processor port line must be switched to an input before

this happens to avoid a conflict.

In the Typical Applications section, there is an example of

interfacing the LTC1298 with DIN and DOUT tied together to

the Intel 8051 MPU.

OUTPUT CODE

•

1 1 1 1 1 1 1 1 1 1 1 1 1 1

1 1 1 1 1 1 1 1 1 1 1 1 1 0

0 0 0 0 0 0 0 0 0 0 0 0 0 1

0 0 0 0 0 0 0 0 0 0 0 0 0 0

INPUT VOLTAGE

VREF – 1LSB

VREF – 2LSB

•

1LSB

INPUT VOLTAGE

(VREF = 5.000V)

4.99878V

4.99756V

•

0.00122V

LTC1286/98 • AI05

Transfer Curve

VREF

4096

VIN

0 0 0 0 0 0 0 0 0 0 0 1

0 0 0 0 0 0 0 0 0 0 0 0

1 1 1 1 1 1 1 1 1 1 1 1

1 1 1 1 1 1 1 1 1 1 1 0

•

LTC1286/98 • AI04

1LSB =

MUX ADDRESS

SGL/DIFF

ODD/SIGN

CHANNEL #

–

GND

–

SINGLE-ENDED

MUX MODE

DIFFERENTIAL

MUX MODE

LTC1096/8 • AI03

SGL/

DIFF

ODD/

SIGN

MSBF

START

MUX

ADDRESS

MSB FIRST/

LSB FIRST

LTC1096/9 • AI02

LTC1298 Channel Selection

Output Code

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