Rainbow Electronics MAX1111 - Manual (Page 11)

MAX1110/MAX1111
+2.7V, Low-Power, Multichannel,
Serial 8-Bit ADCs
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in control bytes of $FF (hex), which trigger single-
ended, unipolar conversions on CH7 (MAX1110) or
CH3 (MAX1111) in external clock mode without power-
ing down between conversions. In external clock mode,
the SSTRB output pulses high for two clock periods
before the most significant bit of the 8-bit conversion
result is shifted out of DOUT. Varying the analog input
alters the output code. A total of 10 clock cycles is
required per conversion. All transitions of the SSTRB
and DOUT outputs occur on SCLK’s falling edge.
How to Start a Conversion
A conversion is started by clocking a control byte into
DIN. With CS low, each rising edge on SCLK clocks a bit
from DIN into the MAX1110/MAX1111’s internal shift reg-
ister. After CS falls, the first arriving logic “1” bit at DIN
defines the MSB of the control byte. Until this first start bit
arrives, any number of logic “0” bits can be clocked into
DIN with no effect. Table 3 shows the control-byte format.
The MAX1110/MAX1111 are compatible with MICROWIRE,
SPI, and QSPI devices. For SPI, select the correct clock
polarity and sampling edge in the SPI control registers:
set CPOL = 0 and CPHA = 0. MICROWIRE, SPI, and
QSPI all transmit a byte and receive a byte at the same
time. Using the Typical Operating Circuit (Figure 3), the
simplest software interface requires three 8-bit transfers
to perform a conversion (one 8-bit transfer to configure
the ADC, and two more 8-bit transfers to clock out the
8-bit conversion result). Figure 6 shows the MAX1110/
MAX1111 common serial-interface connections.
1µF 0.1µF
V DD
DGND
AGND
CS
SCLK
DIN
DOUT
SSTRB
SHDN
+3V
N.C.
0.01µF
CH7 (CH3)
COM
REFOUT
REFIN
C1
1µF
0V TO
+2.048V
ANALOG
INPUT
OSCILLOSCOPE
CH1 CH2 CH3 CH4
*FULL-SCALE ANALOG INPUT, CONVERSION RESULT = $FF (HEX)
( ) ARE FOR THE MAX1111.
MAX1110
MAX1111
+3V
500kHz
OSCILLATOR
SCLK
SSTRB
DOUT*
Figure 5. Quick-Look Circuit
Table 4. Full-Scale and Zero-Scale Voltages
UNIPOLAR MODE
V REFIN + COM
+V REFIN / 2
+ COM
Full Scale
COM COM
-V REFIN / 2
+ COM
Positive
Full Scale
Zero Scale
Zero
Scale
BIPOLAR MODE
Negative
Full Scale