2-Wire Serial 8-Bit DACs with

Rail-to-Rail Outputs

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9

these devices may share the bus. The MAX519 has 16

possible slave addresses. The eighth bit (LSB) in the

slave address byte should be low when writing to the

MAX517/MAX518/MAX519.

The MAX517/MAX518/MAX519 monitor the bus continu-

ously, waiting for a START condition followed by their

slave address. When a device recognizes its slave

address, it is ready to accept data.

The Command Byte and Output Byte

A command byte follows the slave address. Figure 7

shows the format for the command byte. A command

byte is usually followed by an output byte unless it is

the last byte in the transmission. If it is the last byte, all

bits except PD (power-down) and RST (reset) are

ignored. If an output byte follows the command byte,

A0 of the command byte indicates the digital address

of the DAC whose input data latch receives the digital

output data. Set this bit to 0 when writing to the

MAX517. The data is transferred to the DAC’s output

latch during the STOP condition following the transmis-

sion. This allows both DACs of the MAX518/MAX519 to

be updated simultaneously (Figure 8).

Setting the PD bit high powers down the MAX517/

MAX518/MAX519 following a STOP condition (Figure

9a). If a command byte with PD set high is followed by

an output byte, the addressed DAC’s input latch will be

updated and the data will be transferred to the DAC’s

output latch following the STOP condition (Figure 9b).

SCL

SDA

0

0

1 or

AD3

1 or

AD2

10

AD1

AD0

LSB

ACK

SLAVE ADDRESS

Figure 6. Address Byte

SLAVE ADDRESS BITS AD0, AD1, AD2, AND AD3 CORRESPOND TO THE LOGIC

STATE OF THE ADDRESS INPUT PINS.

LSB

MSB

SDA

SCL

R2

R1

R0

RST

PD

X

X

A0/0

ACK

Figure 7. Command Byte

R2, R1, R0: RESERVED BITS. SET TO 0.

RST: RESET BIT, SET TO 1 TO RESET ALL DAC REGISTERS.

PD: POWER-DOWN BIT. SET TO 1 TO PLACE THE DEVICE IN THE 4µA SHUTDOWN

MODE. SET TO 0 TO RETURN TO THE NORMAL OPERATIONAL STATE.

A0: ADDRESS BIT. DETERMINES WHICH DAC'S INPUT LATCH RECEIVES THE 8 BITS

OF DATA IN THE NEXT BYTE. SET TO 0 FOR MAX517.

ACK: ACKNOWLEDGE BIT. THE MAX517/MAX518/MAX519 PULLS SDA LOW DURING

THE 9TH CLOCK PULSE.

X: DON’T CARE.

START CONDITION

STOP CONDITION

OUTPUT BYTE

COMMAND BYTE

SLAVE ADDRESS BYTE

SCL

SDA

MSB

MSB

MSB

LSB

LSB

LSB

ACK

ACK

ACK

Figure 4. A Complete Serial Transmission

SCL

SDA

START CONDITION

STOP CONDITION

Figure 5. All communications begin with a START condition and

end with a STOP condition, both generated by a bus master.