ADS7828

12

SBAS181C

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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

A1

100

1

0

A0

R

A

00

00

D11 D10 D9 D8

AD7 D6 . . .D1 D0

NP

SA1

10

010

A0

W

ASD

C2 C1 C0 PD1 PD0 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.

MSB

6

5

43

21

LSB

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.