Datasheet

ADS7828
11
SBAS181C
www.ti.com
ADDRESS BYTE COMMAND BYTE
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 A1-A0 Address Inputs can be connected to V
DD
or digital
ground. The device address is set by the state of these pins
upon power-up of the ADS7828.
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.
MSB654321LSB
SD C2 C1 C0 PD1 PD0 X X
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.
MSB654321LSB
10010A1A0R/W
PD1 PD0 DESCRIPTION
0 0 Power Down Between A/D Converter Conversions
0 1 Internal Reference OFF and A/D Converter ON
1 0 Internal Reference ON and A/D Converter OFF
1 1 Internal Reference ON and A/D Converter ON
CHANNEL SELECTION CONTROL
SD C2 C1 C0 CH0 CH1 CH2 CH3 CH4 CH5 CH6 CH7 COM
0000+IN–IN —————— —
0001——+IN –IN ———— —
0010————+IN –IN —— —
0011——————+IN –IN —
0100–IN +IN —————— —
0101——–IN +IN ———— —
0110————–IN +IN —— —
0111——————–IN +IN —
1000+IN———————–IN
1001——+IN —— —— — –IN
1010————+IN —— — –IN
1011——————+IN —–IN
1100— +IN ——————–IN
1101———+IN ———— –IN
1110—————+IN —— –IN
1111———————+IN –IN
TABLE II. Channel Selection Control Addressed by Command Byte.
TABLE I. Power-Down Selection