ADC12138CIWM datasheet(29/41 Pages) NSC

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Application Hints (Continued)

be queried to see what mode it is in. This is done by issuing

a “read STATUS register” instruction to the ADC. When bit 9

of the status register is high, the ADC is in test mode; when

bit 9 is low the ADC, is in user mode. As an alternative to cy-

cling the power supply, an instruction sequence may be used

to return the device to user mode. This instruction sequence

must be issued to the ADC using CS. The following table lists

the instructions required to return the device to user mode:

Instruction

DI Data

DI0 DI1 DI2 DI3 DI4 DI5 DI6 DI7

TEST MODE

HHHH

Reset

Test Mode

Instructions

LLLL

LHLHL

LHLH

USER

MODE

LLLL

HHHH

Power Up

LHLHL

Set DO with

or without

Sign

Set

Acquisition

Time

Start

HHHH

HHH

orororor

Conversion

LLLL

LLL

X = Don’t Care

After returning to user mode with the user mode instruction

the power up, data with or without sign, and acquisition time

instructions need to be resent to ensure that the ADC is in

the required state before a conversion is started.

1.7 Reading the Data Without Starting a Conversion

The data from a particular conversion may be accessed

without starting a new conversion by ensuring that the

CONV line is taken high during the I/O sequence. See the

Read Data timing diagrams.

Table 5 describes the operation

of the CONV pin.

2.0 DESCRIPTION OF THE ANALOG MULTIPLEXER

For the ADC12138, the analog input multiplexer can be con-

figured with 4 differential channels or 8 single ended chan-

nels with the COM input as the zero reference or any combi-

nation thereof (see

Figure 9). The difference between the

voltages on the V

REF

+ and V

REF

− pins determines the input

voltage span (V

REF). The analog input voltage range is 0 to

+. Negative digital output codes result when V

−

> V

The actual voltage at V

− or V

+ cannot go below AGND.

CH0, CH2, CH4, and CH6 can be assigned to the MUX-

OUT1 pin in the differential configuration, while CH1, CH3,

CH5, and CH7 can be assigned to the MUXOUT2 pin. In the

differential configuration, the analog inputs are paired as fol-

lows: CH0 with CH1, CH2 with CH3, CH4 with CH5 and CH6

with CH7. The A/DIN1 and A/DIN2 pins can be assigned

positive or negative polarity.

With the single-ended multiplexer configuration CH0 through

CH7 can be assigned to the MUXOUT1 pin. The COM pin is

always assigned to the MUXOUT2 pin. A/DIN1 is assigned

as the positve input; A/DIN2 is assigned as the negative in-

put. (See

Figure 10).

DS012079-34

DS012079-35

FIGURE 9.

Differential

Configuration

DS012079-36

A/DIN1 and A/DIN2 can be assigned as the + or − input

Single-Ended

Configuration

DS012079-37

A/DIN1 is + input

A/DIN2 is − input

FIGURE 10.

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