Rainbow Electronics MAX1092 - Manual (Page 11)

MAX1090/MAX1092
400ksps, +5V, 8-/4-Channel, 10-Bit ADCs
with +2.5V Reference and Parallel Interface
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Table 1. Control Byte Functional Description
NAME FUNCTION
D4
0
SGL/DIF
SGL/DIF = 0: Pseudo-Differential Analog Input Mode
SGL/DIF = 1: Single-Ended Analog Input Mode
In single-ended mode, input signals are referred to COM. In pseudo-differential mode, the voltage
difference between two channels is measured (Tables 2 and 3).
1 0
D3 UNI/BIP
Standby Power-Down Mode. Clock mode is unaffected.
0
1 1
UNI/BIP = 0: Bipolar Mode
UNI/BIP = 1: Unipolar Mode
In unipolar mode, an analog input signal from 0 to V
REF can be converted; in bipolar mode, the
signal can range from -V REF /2 to +V REF /2.
D2, D1, D0
Normal Operation Mode. External clock mode is selected.
1
A2, A1, A0
Address bits A2–A0 select which of the 8/4 (MAX1090/MAX1092) channels is to be converted
(Tables 3 and 4).
Normal Operation Mode. Internal clock mode is selected.
BIT
PD1, PD0
0
D7, D6
PD1 and PD0 select the various clock and power-down modes.
Full Power-Down Mode. Clock mode is unaffected.
D5 ACQMOD
ACQMOD = 0: Internal Acquisition Mode
ACQMOD = 1: External Acquisition Mode
sition interval or initiate a combined acquisition plus
conversion. The sampling interval occurs at the end of
the acquisition interval. The ACQMOD (acquisition
mode) bit in the input control byte (Table 1) offers two
options for acquiring the signal: an internal and an
external acquisition. The conversion period lasts for 13
clock cycles in either the 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 acquisition interval (three external clock
cycles or approximately 1µs in internal clock mode)
ends (Figure 4). When the internal acquisition is com-
bined with the internal clock, the aperture jitter can be
as high as 200ps. Internal clock users wishing to
achieve the 50ps jitter specification should always use
external acquisition mode.
External Acquisition
Use external acquisition mode for precise control of the
sampling aperture and/or dependent control of acquisi-
tion 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 (all other bits in
the control byte are unchanged), terminates acquisition
and starts conversion on WR rising edge (Figure 5).
The address bits for the input multiplexer 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 the Power-Down
Modes section). Changing other bits in the control byte
will corrupt the conversion.
Reading a Conversion
A standard interrupt signal, INT, is provided to allow the
MAX1090/MAX1092 to flag the µP when the conversion
has ended and a valid result is available. INT goes low
when the conversion is complete and the output data
is ready (Figures 4 and 5). INT returns high on the first
read cycle or if a new control byte is written.
Selecting Clock Mode
The MAX1090/MAX1092 operate with an internal or
external clock. Control bits D6 and D7 select either
internal or external clock mode. The part retains the
last-requested clock mode if a power-down mode is
selected in the current input word. For both internal and
external clock modes, internal or external acquisition