AD7778_15 Datasheet, PDF (6/12 Pages) Analog Devices – LC MOS High Speed 1. 4 and 8 Channel 10 Bit ADCs

AD7776/AD7777/AD7778
CONTROL REGISTER
The control register is 10-bit wide and can only be written to.
On power-on, all locations in the control register are automati-
cally loaded with 0s. For the single channel AD7776, locations
CR0 to CR6 of the control register are “don’t cares.” For the
quad channel AD7777, locations CR2 and CR5 are “don’t
cares.” Individual bit functions are described below.
CR0–CR2: Channel Address Locations. Determines which channel
is selected and converted for single-channel operation. For simulta-
neous sampling operation, CR0–CR2 holds the address of one of
the two channels to be sampled.
AD7776
CR2 CR1 CR0
X* X X
*X = Don’t Care
Function
Select A_IN1
AD7777
CR2 CR1 CR0
X* 0 0
X0 1
X1 0
X1 1
*X = Don’t Care
Function
Select A_IN1
Select A_IN2
Select A_IN3
Select A_IN4
AD7778
CR2 CR1
00
00
01
01
10
10
11
11
CR0
0
1
0
1
0
1
0
1
Function
Select A_IN1
Select A_IN2
Select A_IN3
Select A_IN4
Select A_IN5
Select A_IN6
Select A_IN7
Select A_IN8
CR3–CR5: Channel Address Locations. Only applicable for simul-
taneous sampling with the AD7777 or AD7778 when CR3–CR5
holds the address of the second channel to be sampled.
AD7777
CR5 CR4 CR3
X* 0
0
X0 1
X1 0
X1 1
*X = Don’t Care
Function
Select A_IN1
Select A_IN2
Select A_IN3
Select A_IN4
AD7778
CR5 CR4
00
00
01
01
10
10
11
11
CR3
0
1
0
1
0
1
0
1
Function
Select A_IN1
Select A_IN2
Select A_IN3
Select A_IN4
Select A_IN5
Select A_IN6
Select A_IN7
Select A_IN8
CR6: Determines whether operation is on a single channel or
simultaneous sampling on two channels. Location CR6 is a
“don’t care” for the AD7776.
CR6 Function
0 Single channel operation. Channel select
address is contained in locations CR0–CR2.
1 Two channels simultaneously sampled
and sequentially converted. Channel
select addresses contained in locations
CR0–CR2 and CR3–CR5.
CR7: Determines whether the device is in the normal operating
mode or in the half-scale test mode.
CR7 Function
0 Normal Operating Mode
1 Half-Scale Test Mode
In the half-scale test mode, REFIN is internally connected as an
analog input(s). In this mode, locations CR0–CR2 and CR3–CR5
are all “don’t cares” since it is REFIN which is converted. For
the AD7777 and AD7778, the contents of location CR6 still
determine whether a single or a double conversion is carried out
on the REFIN level.
CR8: Determines whether the device is in the normal operating
mode or in the power-down mode.
CR8 Function
0 Normal Operating Mode
1 Power-Down Mode
In the power-down mode all linear circuitry is turned off and the
REFOUT output is weakly (5 kΩ) pulled to AGND. The input
impedance of the analog inputs and of the REFIN input remains
the same in either normal mode or power-down mode. See
under Circuit Description—Power-Down Mode.
CR9: Determines whether BUSY/INT output flag goes low and
remains low during conversion(s) or else goes low and remains
low after the conversion(s) is (are) complete.
CR9 BUSY/INT Functionality
0 Output goes low and remains low during
conversion(s).
1 Output goes low and remains low after conversion(s)
is (are) complete.
–6–
REV. A