The ADS7807 will begin tracking the input signal at the end
of the conversion. Allowing 25µs between convert com-
mands assures accurate acquisition of a new signal. Refer to
Tables II and III for a summary of
CS
,
R/C,
and
BUSY
states,
and Figures 2 through 6 for timing diagrams.
CS
1
↓
0
0
↓
↓
0
0
R/C
X
0
↓
1
1
1
↑
0
BUSY
X
1
1
↑
1
0
0
↑
OPERATION
None. Databus is in Hi-Z state.
Initiates conversion ‘n’. Databus remains
in Hi-Z state.
Initiates conversion ‘n’. Databus enters Hi-Z
state.
Conversion ‘n’ completed. Valid data from
conversion ‘n’ on the databus.
Enables databus with valid data from
conversion ‘n’.
Enables databus with valid data from
conversion ‘n – 1’
(1)
. Conversion n in progress.
Enables databus with valid data from
conversion ‘n – 1’
(1)
. Conversion ‘n’ in progress.
New conversion initiated without acquisition
of a new signal. Data will be invalid. CS and/or
R/C must be HIGH when BUSY goes HIGH.
New convert commands ignored. Conversion
‘n’ in progress.
CS
and
R/C
are internally OR’ed and level triggered. There
is not a requirement which input goes LOW first when
initiating a conversion. If, however, it is critical that
CS
or
R/C
initiates conversion ‘n’, be sure the less critical input is LOW
at least 10ns prior to the initiating input. If
EXT/INT
(pin 8) is
LOW when initiating conversion ‘n’, serial data from conver-
sion ‘n – 1’ will be output on SDATA (pin 19) following the
start of conversion ‘n’. See Internal Data Clock in the Read-
ing Data section.
To reduce the number of control pins,
CS
can be tied LOW
using
R/C
to control the read and convert modes. This will
have no effect when using the internal data clock in the serial
output mode. The parallel output and the serial output (only
when using an external data clock), however, will be affected
whenever
R/C
goes HIGH. Refer to the Reading Data
section.
READING DATA
The ADS7807 outputs serial or parallel data in Straight Binary
(SB) or Binary Two’s Complement data output format. If
SB/BTC
(pin 7) is HIGH, the output will be in SB format, and
if LOW, the output will be in BTC format. Refer to Table IV for
ideal output codes.
The parallel output can be read without affecting the internal
output registers; however, reading the data through the serial
port will shift the internal output registers one bit per data
X
X
0
NOTE: (1) See Figures 2 and 3 for constraints on data valid from
conversion ‘n – 1’.
TABLE II. Control Functions When Using Parallel Output
(DATACLK tied LOW,
EXT/INT
tied HIGH).
CS
↓
0
↓
0
↓
↓
0
0
X
R/C
0
↓
0
↓
1
1
↑
0
X
BUSY
1
1
1
1
1
0
0
↑
0
EXT/INT
0
0
1
1
1
1
1
X
X
DATACLK
Output
Output
Input
Input
Input
Input
Input
X
X
OPERATION
Initiates conversion ‘n’. Valid data from conversion ‘n – 1’ clocked out on SDATA.
Initiates conversion ‘n’. Valid data from conversion ‘n – 1’ clocked out on SDATA.
Initiates conversion ‘n’. Internal clock still runs conversion process.
Initiates conversion ‘n’. Internal clock still runs conversion process.
Conversion ‘n’ completed. Valid data from conversion ‘n’ clocked out on SDATA synchronized
to external data clock.
Valid data from conversion ‘n – 1’ output on SDATA synchronized to external data clock.
Conversion ‘n’ in progress.
Valid data from conversion ‘n – 1’ output on SDATA synchronized to external data clock.
Conversion ‘n’ in progress.
New conversion initiated without acquisition of a new signal. Data will be invalid. CS and/or R/C
must be HIGH when BUSY goes HIGH.
New convert commands ignored. Conversion ‘n’ in progress.
NOTE: (1) See Figures 4, 5, and 6 for constraints on data valid from conversion ‘n – 1’.
TABLE III. Control Functions When Using Serial Output.
DESCRIPTION
Full-Scale Range
Least Significant Bit (LSB)
±10
305µV
ANALOG INPUT
0V to 5V
76µV
0V to 4V
61µV
DIGITAL OUTPUT
BINARY TWO’S COMPLEMENT
STRAIGHT BINARY
(SB/BTC LOW)
(SB/BTC HIGH)
HEX
BINARY CODE
CODE
7FFF
0000
FFFF
8000
HEX
BINARY CODE
1111 1111 1111 1111
1000 0000 0000 0000
0111 1111 1111 1111
0000 0000 0000 0000
CODE
FFFF
8000
7FFF
0000
+Full-Scale (FS – 1LSB)
Midscale
One LSB Below Midscale
–Full-Scale
9.999695V
0V
–305µV
–10V
4.999924V
2.5V
2.499924V
0V
3.999939V
2V
1.999939V
0V
0111 1111 1111 1111
0000 0000 0000 0000
1111 1111 1111 1111
1000 0000 0000 0000
TABLE IV. Output Codes and Ideal Input Voltages.
8
ADS7807
www.ti.com
SBAS022C
BURR-BROWN [ BURR-BROWN CORPORATION ]
