10-Bit Low Power 2-Wire Interface Serial,

Voltage-Output DAC

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9

low transition on SDA with SCL high. A STOP condition

is a low-to-high transition on SDA while SCL is high

(Figure 2). A START condition from the master signals

the beginning of a transmission to the MAX5811. The

master terminates transmission by issuing a not

acknowledge followed by a STOP condition (see

Acknowledge Bit). The STOP condition frees the bus. If

a repeated START condition (Sr) is generated instead of

a STOP condition, the bus remains active. When a

STOP condition or incorrect address is detected, the

MAX5811 internally disconnects SCL from the serial

interface until the next START condition, minimizing digi-

tal noise and feedthrough.

Early STOP Conditions

The MAX5811 recognizes a STOP condition at any point

during transmission except if a STOP condition occurs in

the same high pulse as a START condition (Figure 3).

clock pulse must separate any START and STOP condi-

tions.

Repeated START Conditions

change of data direction on the bus. Such a change

occurs when a command word is required to initiate a

want to relinquish control of the bus. The MAX5811 ser-

ial interface supports continuous write operations with

change in direction of data flow.

Acknowledge Bit (ACK)

The acknowledge bit (ACK) is the ninth bit attached to

any 8-bit data word. ACK is always generated by the

receiving device. The MAX5811 generates an ACK

when receiving an address or data by pulling SDA low

during the ninth clock period. When transmitting data,

the MAX5811 waits for the receiving device to generate

an ACK. Monitoring ACK allows for detection of unsuc-

cessful data transfers. An unsuccessful data transfer

occurs if a receiving device is busy or if a system fault

has occurred. In the event of an unsuccessful data

transfer, the bus master should reattempt communica-

tion at a later time.

Slave Address

A bus master initiates communication with a slave

device by issuing a START condition followed by the 7-

bit slave address (Figure 4). When idle, the MAX5811

waits for a START condition followed by its slave

address. The serial interface compares each address

value bit by bit, allowing the interface to power down

immediately if an incorrect address is detected. The

LSB of the address word is the Read/Write (R/W) bit.

R/W indicates whether the master is writing to or read-

ing from the MAX5811 (R/W = 0 selects the write condi-

tion, R/W = 1 selects the read condition). After

receiving the proper address, the MAX5811 issues an

ACK by pulling SDA low for one clock cycle.

The MAX5811 has eight different factory/user-pro-

grammed addresses (Table 2). Address bits A6

through A1 are preset, while A0 is controlled by ADD.

Connecting ADD to GND sets A0 = 0. Connecting ADD

MAX5811s to share the same bus.

Write Data Format

In write mode (R/W = 0), data that follows the address

byte controls the MAX5811 (Figure 5). Bits C3–C0 con-

figure the MAX5811 (Table 3). Bits D9–D0 are DAC

data. Bits S1 and S0 are sub-bits and are always zero.

Input and DAC registers update on the falling edge of

SCL during the acknowledge bit. Should the write cycle

be prematurely aborted, data is not updated and the

S

A6A5A4A3A2A1A0

R/W

Figure 4. Slave Address Byte Definition

PART

DEVICE ADDRESS

MAX5811L

GND

0010 000

MAX5811L

0010 001

MAX5811M

GND

0010 010

MAX5811M

0010 011

MAX5811N

GND

0110 100

MAX5811N

0110 101

MAX5811P

GND

1010 100

MAX5811P

1010 101

C3

C2

C1

C0

D9

D8

D7

D6

Figure 5. Command Byte Definition