Using Bit-Pushing to Read the MAX194

The MAX194 may be interfaced using a bit-pushing

algorithm, such as the following:

1) Verify that EOC is low before starting the conversion.

2) Assert CONV low to begin conversion.

3) Wait until EOC becomes high. Conversion has

begun.

4) Set CONV high.

5) Wait until EOC becomes low. Conversion is com-

plete.

6) Assert SCLK low.

7) Assert CS low.

8) Clear the 16-bit result register.

9) Repeat 16 times:

9-1. Set SCLK high.

9-2. Rotate the 16-bit result register left.

9-3. Read DOUT into least significant bit of the

result register.

9-4. Assert SCLK low.

10) Set CS high.

Reset and Calibration Procedure

When the MAX194 is installed in an environment with an

unregulated temperature, thermal variation can cause

DC offset errors. Transients on the power supply or ref-

erence during the power-on calibration are also a

source of DC offset error. These errors can be eliminat-

ed by performing re-calibration, as outlined below:

1) Assert the MAX194 RESET pin low.

2) Run the conversion clock until EOC becomes high.

3) Set the MAX194 RESET pin high.

4) Run the conversion clock until EOC becomes low.

For best accuracy, a typical application circuit should

allow time for the power supply and ambient tempera-

ture to settle before re-calibrating the MAX194. Refer to

the Calibration section of the MAX194 data sheet.

_Detailed Description of Hardware

Jumper Options

Several jumper blocks allow different configurations of

the MAX194. Jumper functions are listed in Table 6.

See the Voltage Reference and Measuring Supply

Current sections.

Data Connector Interface

The 68HC16 module and MAX194 communicate

through the QSPI port on the 40-pin data connector.

Table 7 lists the function of each pin.

MAX194 Evaluation System/Evaluation Kit

6

_______________________________________________________________________________________

Table 6. Jumper Settings

JUMPER

POSITION

FUNCTION

Closed

Ground the SCLK pin.

JU1

Open

Allows the SCLK pin to be driven by

the user.

“OSC”

Conversion clock is driven by crystal

oscillator U4.

“EXT”

Conversion clock is driven by the

EXTCLK input pad.

“QSPI”

Conversion clock is driven by the

QSPI serial clock.

“QSPI”

Connects CS to QSPI chip-select

PCS0.

JU4

“GND”

Connects CS to ground; data output

is always enabled.

“QSPI”

Connects CONV to QSPI chip-select

PCS0.

JU5

“CONT”

Connects CONV to EOC for continu-

ous conversion mode.

Open

Normal operating mode.

JU6

Closed

Momentary closure resets and

re-calibrates the MAX194. Do not

close this jumper if the µC module is

connected.

“SHDN”

Select shutdown mode.

“AUTO”

Lets 68HC16 drive the BP/UP/SHDN

pin. If no µC is connected, bipolar

input mode is selected.

“UNI”

Select unipolar mode.

JU7

Open

Select bipolar mode.

JU3

Table 5. QSPI Receive Format for MAX194

ADDR

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

RR0

x

x

x

x

x

x

x

x

B13

B12

B11

B10

B9

B8

B7

B6

RR1

x

x

x

x

x

x

B5

B4

B3

B2

B1

B0

sub

sub

x

x