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DAC7574

SLAS375 – JUNE 2003

Master Receiver Reading From a Slave Transmitter (DAC7574) in HS-Mode

When reading data to the DAC7574 in HS-MODE, the master begins to transmit, what is called the HS-Master

Code

(0000 1XXX) in F/S-mode. No device is allowed to acknowledge the HS-Master Code, so the HS-Master

Code

is followed by a NOT acknowledge.

The Master then switches to HS-mode and issues a REPEATED START condition, followed by the address byte

(with R/W = 0) after which the DAC7574 acknowledges by pulling SDA low. This address byte is usually followed

by the control byte, which is also acknowledged by the DAC7574.

Then there is a REPEATED START condition initiated by the master and the address is resent with (R/W = 1).

This is acknowledged by the DAC7574, indicating that it is prepared to transmit data. Two or Three bytes of data

are then read back from the DAC7574, depending on the (PD0-Bit). The value of Buff-Sel1 and Buff-Sel0

determines, which channel data is read back. A STOP condition follows.

With the (PD0-Bit = 0) the DAC7574 transmits 2 bytes of data, HIGH-BYTE followed by LOW-BYTE (refer to

Table 7 HS-Mode Readback Sequence).

With the (PD0-Bit = 1) the DAC7574 transmits 3 bytes of data, POWER-DOWN-BYTE followed by the

HIGH-BYTE

followed by the LOW-BYTE (refer to Table 7 HS-Mode Readback Sequence).

Table 7. Master Receiver Reading Slave Transmitter (DAC7574) in HS-Mode

HS MODE READBACK SEQUENCE

Transmitter

MSB

6

5

4

3

2

1

LSB

Comment

Master

Start

Begin sequence

Master

0

0

0

0

1

X

X

X

HS Mode Master Code

No device may acknowledge HS

NONE

Not Acknowledge

master code

Master

Repeated Start

Master

1

0

0

1

1

A1

A0

R/W

Write addressing (R/W=0)

DAC7574

DAC7574 Acknowledges

Master

0

0

Load 1

Load 0

X

Buff Sel 1

Buff Sel 0

PD0

Control byte (PD0 = 1)

DAC7574

DAC7574 Acknowledges

Master

Repeated Start

Master

1

0

0

1

1

A1

A0

R/W

Read addressing (R/W=1)

DAC7574

DAC7574 Acknowledges

DAC7574

PD1

PD2

1

1

1

1

1

1

Power-down byte

Master

Master Acknowledges

DAC7574

D11

D10

D9

D8

D7

D6

D5

D4

Reading data word, high byte

Master

Master Acknowledges

DAC7574

D3

D2

D1

D0

x

x

x

x

Reading data word, low byte

Master

Master Not Acknowledges

Master signal end of read

Master

Stop or Repeated Start

Done

Power-On Reset

The DAC7574 contains a power-on-reset circuit that controls the output voltage during power up. On power up,

the DAC register is filled with zeros and the output voltage is 0 V; it remains there until a valid write sequence is

made to the DAC. This is useful in applications where it is important to know the state of the output of the DAC

while it is in the process of powering up. No device pin should be brought high before supply is applied.

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