ADDRESS BYTE
COMMAND BYTE
MSB
1
6
0
5
0
4
1
3
0
2
1
LSB
R/W
MSB
SD
6
5
4
3
2
1
LSB
X
A1
A0
C2
C1
C0
PD1
PD0
X
The address byte is the first byte received following the
START condition from the master device. The first five bits
(MSBs) of the slave address are factory pre-set to 10010.
The next two bits of the address byte are the device select
bits, A1 and A0. Input pins (A1-A0) on the ADS7828 deter-
mine these two bits of the device address for a particular
ADS7828. A maximum of four devices with the same pre-set
code can therefore be connected on the same bus at one
time.
The ADS7828 operating mode is determined by a command
byte which is illustrated above.
SD: Single-Ended/Differential Inputs
0: Differential Inputs
1: Single-Ended Inputs
C2 - C0: Channel Selections
PD1 - 0: Power-Down Selection
X: Unused
See Table I for a power-down selection summary.
See Table II for a channel selection control summary.
The A1-A0 Address Inputs can be connected to VDD or digital
ground. The device address is set by the state of these pins
upon power-up of the ADS7828.
PD1 PD0
DESCRIPTION
The last bit of the address byte (R/W) defines the operation
to be performed. When set to a ‘1’ a read operation is
selected; when set to a ‘0’ a write operation is selected.
Following the START condition the ADS7828 monitors the
SDA bus, checking the device type identifier being transmit-
ted. Upon receiving the 10010 code, the appropriate device
select bits, and the R/W bit, the slave device outputs an
acknowledge signal on the SDA line.
0
0
1
1
0
1
0
1
Power Down Between A/D Converter Conversions
Internal Reference OFF and A/D Converter ON
Internal Reference ON and A/D Converter OFF
Internal Reference ON and A/D Converter ON
TABLE I. Power-Down Selection
CHANNEL SELECTION CONTROL
SD
C2
C1
C0
CH0
CH1
CH2
CH3
CH4
CH5
CH6
CH7
COM
0
0
0
0
0
0
0
0
1
1
1
1
1
1
1
1
0
0
0
0
1
1
1
1
0
0
0
0
1
1
1
1
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
+IN
—
–IN
—
—
+IN
—
—
–IN
—
—
—
—
—
—
—
—
—
—
—
—
—
+IN
—
–IN
—
—
—
—
—
—
—
—
+IN
—
–IN
—
—
–IN
—
+IN
—
—
—
—
—
—
–IN
—
+IN
—
—
—
—
—
—
—
—
–IN
—
+IN
—
—
—
—
—
—
—
—
–IN
—
+IN
—
—
+IN
—
—
—
—
—
—
–IN
–IN
–IN
–IN
–IN
–IN
–IN
–IN
—
+IN
—
—
—
—
—
—
—
—
—
+IN
—
—
—
—
—
—
—
—
—
+IN
—
—
—
+IN
—
—
—
—
—
—
—
—
+IN
—
—
—
—
—
—
—
—
—
+IN
—
—
—
—
—
—
—
—
—
+IN
TABLE II. Channel Selection Control Addressed by Command Byte.
ADS7828
SBAS181C
11
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