ADS7828

10

SBAS181B

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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.

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.

MSB

654321

LSB

SD

C2

C1

C0

PD1

PD0

X

X

The ADS7828’s operating mode is determined by a com-

mand 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 Truth Table.

MSB

654321

LSB

10010

A1

A0

R/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

POWER-DOWN SELECTION

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.

CHANNEL SELECTION CONTROL

SD

C2

C1

C0

CH0

CH1

CH2

CH3

CH4

CH5

CH6

CH7

COM

00

0

0

+IN

–IN

—

—

——

——

—

00

0

1

——

+IN

–IN

——

——

—

00

1

0

—

———

+IN

–IN

——

—

00

1

1

—

———

—

—

+IN

–IN

—

01

0

0

–IN

+IN

—

—

——

——

—

01

0

1

——

–IN

+IN

——

——

—

01

1

0

—

———

–IN

+IN

——

—

01

1

1

—

———

—

—

–IN

+IN

—

10

0

0

+IN

—

—

—

——

——

–IN

10

0

1

——

+IN

——

—

—

—

–IN

10

1

0

—

———

+IN

——

—

–IN

10

1

1

—

———

—

—

+IN

—–IN

11

0

0

—

+IN

—

—

——

——

–IN

11

0

1

——

—

+IN

——

——

–IN

11

1

0

—

———

—

+IN

——

–IN

11

1

1

—

———

—

—

—

+IN

–IN

TABLE I. Channel Selection Control Addressed by Command BYTE.