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Master Receiver Reading From a Slave Transmitter (DAC5574) in HS-Mode

Power-On Reset

Power-Down Modes

DAC5574

SLAS407 – DECEMBER 2003

When reading data to the DAC5574 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 DAC5574 acknowledges by pulling SDA low. This address byte is usually followed

by the control byte, which is also acknowledged by the DAC5574.

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 DAC5574, indicating that it is prepared to transmit data. Two or Three bytes of data

are then read back from the DAC5574, 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 DAC5574 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 DAC5574 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 (DAC5574) 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)

DAC5574

DAC5574 Acknowledges

Master

0

0

Load 1

Load 0

X

Buff Sel 1

Buff Sel 0

PD0

Control byte (PD0 = 1)

DAC5574

DAC5574 Acknowledges

Master

Repeated Start

Master

1

0

0

1

1

A1

A0

R/W

Read addressing (R/W=1)

DAC5574

DAC5574 Acknowledges

DAC5574

PD1

PD2

1

1

1

1

1

1

Power-down byte

Master

Master Acknowledges

DAC5574

D7

D6

D5

D4

D3

D2

D1

D0

Reading data word, high byte

Master

Master Acknowledges

DAC5574

x

x

x

x

x

x

x

x

Reading data word, low byte

Master

Master Not Acknowledges

Master signal end of read

Master

Stop or Repeated Start

Done

The DAC5574 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.

The DAC5574 contains four separate power-down modes of operation. The modes are programmable via two

most significant bits of the MSB byte, while (CTRL[0] = PD0 = 1). Table 8 shows how the state of these bits

correspond to the mode of operation of the device.

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