MSB
6
5
4
3
2
1
LSB
INITIATING CONVERSION
BYTE 0
BYTE 1
0
0
0
0
D11
D3
D10
D2
D9
D1
D8
D0
Provided the master has write-addressed it, the ADS7828
turns on the A/D converter’s section and begins conversions
when it receives BIT 4 of the command byte shown in the
Command Byte. If the command byte is correct, the ADS7828
will return an ACK condition.
D7
D6
D5
D4
READING IN F/S MODE
Figure 3 describes the interaction between the master and
the slave ADS7828 in Fast or Standard (F/S) mode. At the
end of reading conversion data the ADS7828 can be issued
a repeated START condition by the master to secure bus
operation for subsequent conversions of the A/D converter.
This would be the most efficient way to perform continuous
conversions.
READING DATA
Data can be read from the ADS7828 by read-addressing the
part (LSB of address byte set to 1) and receiving the
transmitted bytes. Converted data can only be read from the
ADS7828 once a conversion has been initiated as described
in the preceding section.
Each 12-bit data word is returned in two bytes, as shown
below, where D11 is the MSB of the data word, and D0 is the
LSB. Byte 0 is sent first, followed by Byte 1.
ADC Power-Down Mode
ADC Sampling Mode
S
1
0
0
1
0
A
A
W
A
SD
C
C
C
PD PD X
0
X
A
1
0
2
1
0
1
Command Byte
Write-Addressing Byte
ADC Power-Down Mode
(depending on power-down selection bits)
ADC Converting Mode
Sr
1
0
0
1
0
A
A
R
A
0
0
0
0
D
D
D
D
A
D
D
.D
D
0
N
P
1
0
11 10
9
8
7
6 . .
1
See Note (1)
Read-Addressing Byte
2 x (8 Bits + ack/not-ack)
A = acknowledge (SDA LOW)
N = not acknowledge (SDA HIGH)
S = START Condition
P = STOP Condition
Sr = repeated START condition
W = '0' (WRITE)
R = '1' (READ)
From Master to Slave
From Slave to Master
NOTE: (1) To secure bus operation and loop back to the stage of write-addressing for next conversion, use repeated START.
FIGURE 3. Typical Read Sequence in F/S Mode.
ADS7828
SBAS181C
12
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