Datasheet

AD7864
Rev. D | Page 8 of 28
Pin No. Mnemonic Description
27
INT
/EXT CLK
Internal/External Clock Select Input. When this pin is at Logic 0, the AD7864 uses its internally generated master
clock. When this pin is at Logic 1, the master clock is generated externally to the device.
28 CLKIN Conversion Clock Input. This is an externally applied clock that allows the user to control the conversion rate of
the AD7864. Each conversion needs 14 clock cycles for the conversion to be completed and an
EOC
pulse to be
generated. The clock should have a duty cycle that is no worse than 60/40. See the
section.
Using An External Clock
29 to 34 DB11 to DB6 Data Bit 11 is the MSB, followed by Data Bit 10 to Data Bit 6. Three-state TTL outputs. Output coding is twos
complement for the AD7864-1 and AD7864-3. Output coding is straight (natural) binary for the AD7864-2.
35 DV
DD
Positive Supply Voltage for Digital Section, 5.0 V ± 5%. Connect a 0.1 μF decoupling capacitor between this pin
and AGND. Both DV
DD
and AV
DD
should be externally tied together.
36 V
DRIVE
This pin provides the positive supply voltage for the output drivers (DB0 to DB11), BUSY,
EOC
, and FRSTDATA. It
is normally tied to DV
DD
. Decouple V
DRIVE
with a 0.1 μF capacitor to improve performance when reading during
the conversion sequence. To facilitate interfacing to 3 V processors and DSPs, the output data drivers can also be
powered by a 3 V ± 10% supply.
37 DGND Digital Ground. This is the ground reference for digital circuitry. Connect this DGND pin to the AGND plane of
the system at the AGND pin.
38, 39 DB5, DB4 Data Bit 5 to Data Bit 4. Three-state TTL outputs.
40 to 43 DB3 to DB0 Data Bit 3 to Data Bit 0. Bidirectional data pins. When a read operation takes place, these pins are three-state TTL
outputs. The channel select register is programmed with the data on the DB0 to DB3 pins with standard
CS
and
WR
signals. DB0 represents Channel 1, and DB3 represents Channel 4.
44
EOC
End-of-Conversion. Active low logic output indicating conversion status. The end of each conversion in a
conversion sequence is indicated by a low-going pulse on this line.