MAX1021 datasheet(34/47 Pages) MAXIM

34 / 47 page

10-Bit, Multichannel ADCs/DACs with FIFO,

Temperature Sensing, and GPIO Ports

______________________________________________________________________________________

Partial Reads and Partial Writes

If the first byte of an entry in the FIFO is partially read

(CS is pulled high after fewer than eight SCLK cycles),

the remaining bits are lost for that byte. The next byte of

data that is read out contains the next 8 bits. If the first

byte of an entry in the FIFO is read out fully, but the

second byte is read out partially, the rest of that byte is

lost. The remaining data in the FIFO is unaffected and

can be read out normally after taking CS low again, as

long as the 4 leading bits (normally zeros) are ignored.

If CS is pulled low before EOC goes low, a conversion

may not be completed and the FIFO data may not be

correct. Incorrect writes (pulling CS high before com-

pleting eight SCLK cycles) are ignored and the register

remains unchanged.

Applications Information

Internally Timed Acquisitions and

Conversions Using CNVST

ADC Conversions in Clock Mode 00

In clock mode 00, the wake-up, acquisition, conversion,

and shutdown sequence is initiated through CNVST

and performed automatically using the internal oscilla-

tor. Results are added to the internal FIFO to be read

out later. See Figure 6 for clock mode 00 timing after a

command byte is issued. See Table 5 for details on

programming the clock mode in the setup register.

Initiate a scan by setting CNVST low for at least 40ns

before pulling it high again. The MAX1020–MAX1023/

MAX1057/MAX1058 then wake up, scan all requested

channels, store the results in the FIFO, and shut down.

After the scan is complete, EOC is pulled low and the

results are available in the FIFO. Wait until EOC goes

low before pulling CS low to communicate with the seri-

al interface. EOC stays low until CS or CNVST is pulled

low again. A temperature-conversion result, if request-

ed, precedes all other FIFO results. Temperature

results are available in 12-bit format.

FULL-SCALE

TRANSITION

111....111

INPUT VOLTAGE (LSB)

FS = VREF

111....110

111....101

000....011

000....010

000....001

000....000

1 LSB = VREF / 1024

FS - 3/2 LSB

Figure 3. Unipolar Transfer Function—Full Scale (FS) = VREF

OUTPUT CODE

011....111

TEMPERATURE (°C)

011....110

000....001

111....101

100....001

100....000

111....111

111....110

000....000

000....010

-256

+255.5

Figure 5. Temperature Transfer Function

011....111

-FS

INPUT VOLTAGE (LSB)

FS = VREF / 2 + VCOM

VREF = VREF+ - VREF-

-FS = -VREF / 2

011....110

011....101

000....001

000....000

111....111

100....011

100....010

100....001

100....000

(COM)

-1

+FS - 1 LSB

1 LSB = VREF / 1024

ZS = COM

VREF

(COM)

VREF

Figure 4. Bipolar Transfer Function—Full Scale (±FS) = ±VREF / 2

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