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MAX1240_10 Datasheet, PDF (11/15 Pages) Maxim Integrated Products – +2.7V, Low-Power, 12-Bit Serial ADCs in 8-Pin SO
+2.7V, Low-Power,
12-Bit Serial ADCs in 8-Pin SO
CS
tCS0
SCLK
tDV
DOUT
tAPR
INTERNAL
T/H
(TRACK/ACQUIRE)
tCONV
(HOLD)
…
…
tDO
…
tSTR
…
tCH
tCL
B2
B1
B0
(TRACK/ACQUIRE)
tCS
tTR
Figure 9. Detailed Serial-Interface Timing
End of conversion (EOC) is signaled by DOUT going
high. DOUT’s rising edge can be used as a framing
signal. SCLK shifts the data out of this register any time
after the conversion is complete. DOUT transitions on
SCLK’s falling edge. The next falling clock edge pro-
duces the MSB of the conversion at DOUT, followed by
the remaining bits. Since there are 12 data bits and one
leading high bit, at least 13 falling clock edges are
needed to shift out these bits. Extra clock pulses occur-
ring after the conversion result has been clocked out,
and prior to a rising edge of CS, produce trailing zeros
at DOUT and have no effect on converter operation.
Minimum cycle time is accomplished by using DOUT’s
rising edge as the EOC signal. Clock out the data with
12.5 clock cycles at full speed. Pull CS high after read-
OUTPUT CODE
11…111
11…110
11…101
FULL-SCALE
TRANSITION
FS = VREF - 1LSB
1LSB = VREF
4096
00…011
00…010
00…001
00…000
0
12 3
INPUT VOLTAGE (LSBs)
FS
FS - 3/2LSB
Figure 10. Unipolar Transfer Function, Full Scale (FS) = VREF -
1LSB, Zero Scale (ZS) = GND
ing the conversion’s LSB. After the specified minimum
time (tCS), CS can be pulled low again to initiate the
next conversion.
Output Coding and Transfer Function
The data output from the MAX1240/MAX1241 is binary,
and Figure 10 depicts the nominal transfer function.
Code transitions occur halfway between successive-
integer LSB values. If VREF = +2.500V, then 1 LSB =
610µV or 2.500V/4096.
____________Applications Information
Connection to Standard Interfaces
The MAX1240/MAX1241 serial interface is fully compat-
ible with SPI/QSPI and MICROWIRE standard serial
interfaces (Figure 11).
If a serial interface is available, set the CPU’s serial
interface in master mode so the CPU generates the ser-
ial clock. Choose a clock frequency up to 2.1MHz.
1) Use a general-purpose I/O line on the CPU to pull CS
low. Keep SCLK low.
2) Wait the for the maximum conversion time specified
before activating SCLK. Alternatively, look for a DOUT
rising edge to determine the end of conversion.
3) Activate SCLK for a minimum of 13 clock cycles. The
first falling clock edge produces the MSB of the
DOUT conversion. DOUT output data transitions on
SCLK’s falling edge and is available in MSB-first for-
mat. Observe the SCLK to DOUT valid timing char-
acteristic. Data can be clocked into the µP on
SCLK’s rising edge.
4) Pull CS high at or after the 13th falling clock edge. If
CS remains low, trailing zeros are clocked out after
the LSB.
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