AD1674
GROUNDING
PACKAGE INFORMATION
Dimensions shown in inches and (mm).
0.505 (12.83)
28
15
0.59 ±0.01
(14.98 ±0.254)
1
14
1.42 (36.07)
1.40 (35.56)
0.145 ±0.02
(3.68 ±0.51)
0.125
(3.17)
MIN
0.017 ±0.003
(0.43 ±0.076)
0.1 (2.54)
0.047 ±0.007
(1.19 ±0.178)
0.085
(2.16)
SEATING
PLANE
0.010 ±0.002
(0.254 ±0.05)
0.6 (15.24)
0.050 ±0.010
(1.27 ±0.254)
0.095
(2.41)
PIN 1
GENERAL MICROPROCESSOR INTERFACE
CONSIDERATIONS
A typical A/D converter interface routine involves several opera-
tions. First, a write to the ADC address initiates a conversion.
The processor must then wait for the conversion cycle to com-
plete, since most ADCs take longer than one instruction cycle to
complete a conversion. Valid data can, of course, only be read
after the conversion is complete. The AD1674 provides an out-
put signal (STS) which indicates when a conversion is in
progress. This signal can be polled by the processor by reading
it through an external three-state buffer (or other input port).
The STS signal can also be used to generate an interrupt upon
completion of a conversion, if the system timing requirements
are critical (bear in mind that the maximum conversion time of
the AD1674 is only 10 microseconds) and the processor has
other tasks to perform during the ADC conversion cycle. An-
other possible time-out method is to assume that the ADC will
take 10 microseconds to convert, and insert a sufficient number
of “no-op” instructions to ensure that 10 microseconds of pro-
cessor time is consumed.
Once it is established that the conversion is finished, the data
can be read. In the case of an ADC of 8-bit resolution (or less),
a single data read operation is sufficient. In the case of convert-
ers with more data bits than are available on the bus, a choice of
data formats is required, and multiple read operations are
needed. The AD1674 includes internal logic to permit direct in-
terface to 8-bit or 16-bit data buses, selected by the 12/8 input.
In 16-bit bus applications (12/8 HIGH) the data lines (DB11
through DB0) may be connected to either the 12 most signifi-
cant or 12 least significant hits of the data bus. The remaining
four bits should be masked in software. The interface to an 8-bit
data bus (12/8 LOW) contains the 8 MSBs (DB11 through
DB4). The odd address (A
0
HIGH) contains the 4 LSBs (DB3
through DB0) in the upper half of the byte, followed by four
trailing zeroes, thus eliminating bit masking instructions.
28-Lead Plastic DIP Package (N-28)
28
15
0.550 (13.97)
0.530 (13.462)
PIN 1
1
1.450 (38.83)
1.440 (35.576)
0.200
(5.080)
MAX
14
0.160 (4.06)
0.140 (3.56)
0.606 (15.39)
0.594 (15.09)
0.175 (4.45)
0.120 (3.05)
0.020 (0.508)
0.015 (0.381)
0.105 (2.67)
0.095 (2.41)
0.065 (1.65)
0.045 (1.14) SEATING
PLANE
15
°
0
°
0.012 (0.305)
0.008 (0.203)
28-Lead Wide-Body SO Package (R-28)
28
15
0.2992 (7.60)
0.2914 (7.40)
PIN 1
1
14
0.4193 (10.65)
0.3937 (10.00)
0.0291 (0.74)
x 45
°
0.0098 (0.25)
0.0118 (0.30)
0.0040 (0.10)
0.0500 (1.27)
BSC
0.0192 (0.49)
0.0138 (0.35)
0.0125 (0.32)
0.0091 (0.23)
8
°
0
°
0.0500 (1.27)
0.0157 (0.40)
AD1674 Data Format for 8-Bit Bus
–12–
REV. C
PRINTED IN U.S.A.
0.7125 (18.10)
0.6969 (17.70)
0.1043 (2.65)
0.0926 (2.35)
C1425b–10–3/94
If a single AD1674 is used with separate analog and digital
ground planes, connect the analog ground plane to AGND and
the digital ground plane to DGND keeping lead lengths as short
as possible. Then connect AGND and DGND together at the
AD1674. If multiple AD1674s are used or the AD1674 shares
analog supplies with other components, connect the analog and
digital returns together once at the power supplies rather than at
each chip. This prevents large ground loops which inductively
couple noise and allow digital currents to flow through the ana-
log system.
28-Pin Ceramic DIP Package (D-28)
AD [ ANALOG DEVICES ]
