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AS1539/AS1541

Data Sheet - A p p l i c a t i o n I n f o r m a t i o n

9 Application Information

Initiating a Conversion

After the AS1539/AS1541 has been write-addressed by the bus master, the A/D converter circuitry is powered on, and

conversions will begin when a command byte bit C0 (see Command Byte on page 12) is received. If the address byte

is valid, the AS1539/AS1541 will return an ACK.

Reading Data

Data can be read from the AS1539/AS1541 by read-addressing the device (LSB of address byte set to 1 (see Com-

mand Byte on page 12)) and receiving the transmitted bytes. Converted data can only be read from the AS1539/

AS1541 once a conversion has been initiated as described in Initiating a Conversion.

Each 12-bit data word (see Figure 27) is returned in two bytes, where D9 is the MSB of the data word, and D0 is the

LSB. Byte 0 is sent first, followed by Byte 1.

Figure 27. Data Word

Figure 28 illustrates the interaction between the master and the slave AS1539/AS1541.

The most efficient way to perform continuous conversions is to issue repeated STARTs to the AS1539/AS1541 (to

secure the bus for subsequent ADC conversions) after reading each conversion. It is recommended that during the

conversion mode no data is clocked into the ADC to prevent internal noise. Therefore, after the repeated start com-

mend it is recommanded not to clock in or out any data from the converter for 3.7µs. The ADC powers up after the PD0

bit is clocked in and it takes 1.4µs to fully power up. At a clock frequency of 3.4MHz this time is automatically achieved

and no extra delay should be included.

Figure 28. Read Sequence

Where:

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)

0

0

0

0

D9

D8

D7

D6

MSB

6

5

432

1

LSB

D5

D4

D3

D2

D1

D0

0

0

Byte 0

Byte 1

S

1

0

0

1

0

A1

A0

W

SD

C2

C1

C0 PD1 PD0

X

X

A

A

Sr

1

0

0

1

0

A1

A0

0

0

0

0

D9

D8

D7

D6

A

A

R

D5

0

N

P

D4 ... D0

From Master to Slave

From Slave to Master

ADC Powerdown Mode

ADC Sampling Mode

Write-Addressing Byte

Command Byte

ADC Conversion Mode

Read-Addressing Byte

ADC Powerdown Mode *

* Dependant on powerdown selection bits PD0 and PD1

Use repeated STARTs to secure the

bus operation and loop back to the

stage of write-addressing for the

next conversion.

3.7µs

0