Input Format

The control byte is latched into the device, on pins

D7–D0, during a write cycle. Table 2 shows the control-

byte format.

Output Data Format

The output data format is binary in unipolar mode and

twos-complement binary in bipolar mode. When reading

the output data, CS and RD must be low.

How to Start a Conversion

Conversions are initiated with a write operation, which

selects the mux channel and configures the MAX196/

MAX198 for either a unipolar or bipolar input range. A

write pulse (WR + CS) can either start an acquisition inter-

val or initiate a combined acquisition plus conversion. The

sampling interval occurs at the end of the acquisition

interval. The ACQMOD bit in the input control byte offers

two options for acquiring the signal: internal or external.

The conversion period lasts for 12 clock cycles in either

internal or external clock or acquisition mode.

Writing a new control byte during a conversion cycle will

abort the conversion and start a new acquisition interval.

Internal Acquisition

Select internal acquisition by writing the control byte with

the ACQMOD bit cleared (ACQMOD = 0). This causes

the write pulse to initiate an acquisition interval whose

duration is internally timed. Conversion starts when this

2MHz) ends (see Figure 5).

External Acquisition

Use the external acquisition timing mode for precise con-

trol of the sampling aperture and/or independent control

of acquisition and conversion times. The user controls

acquisition and start-of-conversion with two separate

write pulses. The first pulse, written with ACQMOD = 1,

starts an acquisition interval of indeterminate length. The

second write pulse, written with ACQMOD = 0, termi-

nates acquisition and starts conversion on WR’s rising

edge (Figure 6). However, if the second control byte

contains ACQMOD = 1, an indefinite acquisition interval

is restarted.

The address bits for the input mux must have the same

values on the first and second write pulses. Power-down

mode bits (PD0, PD1) can assume new values on the

second write pulse (see

Power-Down Mode section).

How to Read a Conversion

A standard interrupt signal, INT, is provided to allow the

device to flag the µP when the conversion has ended

and a valid result is available. INT goes low when con-

version is complete and the output data is ready

(Figures 5 and 6). It returns high on the first read cycle

or if a new control byte is written.

Multirange, Single +5V, 12-Bit DAS

with 12-Bit Bus Interface

10

______________________________________________________________________________________

HIGH-Z

HIGH-Z

CS

WR

D7–D0

INT

RD

DOUT

ACQMOD ="0"

DATA VALID

CONTROL

BYTE

Figure 5. Conversion Timing Using Internal Acquisition Mode