Datasheet

ADS7828
12
SBAS181C
www.ti.com
INITIATING CONVERSION
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.
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.
FIGURE 3. Typical Read Sequence in F/S Mode.
Sr A
1
10010 A
0
RA0000D
11
D
10
D
9
D
8
AD
7
D
6 . .
.D
1
D
0
NP
SA
1
10010 A
0
W ASDC
2
C
1
C
0
PD
1
PD
0
XXA
From Master to Slave
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 Slave to Master
Write-Addressing Byte
Command Byte
ADC Power-Down Mode ADC Sampling Mode
ADC Converting Mode
ADC Power-Down Mode
(depending on power-down selection bits)
Read-Addressing Byte 2 x (8 Bits + ack/not-ack)
See Note (1)
NOTE: (1) To secure bus operation and loop back to the stage of write-addressing for next conversion, use repeated START.
MSB6 543 21LSB
BYTE 0 0 0 0 0 D11 D10 D9 D8
BYTE 1 D7 D6 D5 D4 D3 D2 D1 D0
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.