MAX1295 Datasheet, PDF (12/20 Pages) Maxim Integrated Products – 265ksps, +3V, 6-/2-Channel, 12-Bit ADCs with +2.5V Reference and Parallel Interface

265ksps, +3V, 6-/2-Channel, 12-Bit ADCs
with +2.5V Reference and Parallel Interface
t_CS
CS
t_CSWS
WR
D11–D0
t_WR
t_DS
CONTROL
BYTE
ACQMOD = "1"
t_ACQ
t_CSWH
t_CONV
t_DH
CONTROL
BYTE
ACQMOD = "0"
INT
RD
DOUT
HIGH-Z
t_INT1
t_D0
t_TR
VALID DATA
HIGH-Z
Figure 5. Conversion Timing Using 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
control byte 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 pulse.
Power-down mode bits (PD0, PD1) can assume new
values on the second write pulse (see 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
MAX1295/MAX1297 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, 5). It returns high on the first read
cycle or if a new control byte is written.
Selecting Clock Mode
The MAX1295/MAX1297 operate with either an internal
or an 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 mode, internal or external acquisition
can be used. At power-up, the MAX1295/MAX1297
enter the default external clock mode.
Internal Clock Mode
Select internal clock mode to release the µP from the
burden of running the SAR conversion clock. Bits D6
and D7 of the control byte must be set to 1; the internal
clock frequency is then selected, resulting in a conver-
sion time of 3.6µs. When using the internal clock mode,
tie the CLK pin either high or low to prevent the pin
from floating.
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