Read Mode

In the temperature register (see the

Temperature

Register (02h–03h) table), temperature is represented

as a 12-bit code and is accessible at location 02h and

03h. The upper 8 bits are at location 02h and the lower

4 bits are in the upper nibble of the byte at location

03h. Upon power reset, the registers are set to a +25°C

default temperature and the controller starts a tempera-

ture conversion. The temperature register stores new

temperature readings.

The current temperature is loaded into the (user) tem-

write is received and when a word address is received.

Consequently, if the two temperature registers are read

ature conversion to occur between reads, and the

results can be inaccurate. To prevent this from occur-

ring, the registers should be read using a single, multi-

the internal temperature registers.

transmission protocol. A device that sends data onto

the bus is defined as a transmitter and a device receiv-

ing data is defined as a receiver. The device that con-

trols the message is called a master. The devices that

are controlled by the master are slaves. The bus must

be controlled by a master device that generates the

serial clock (SCL), controls the bus access, and gener-

ates the START and STOP conditions. The DS4026

bus are made through the open-drain I/O lines SDA

and SCL. Within the bus specifications, a standard

mode (100kHz maximum clock rate) and a fast mode

(400kHz maximum clock rate) are defined. The DS4026

works in both modes.

The following bus protocol has been defined (Figure 3):

• Data transfer can be initiated only when the bus is

not busy.

10MHz to 51.84MHz TCXO

10

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Table 1. Register Map

ADDRESS

BIT 7

BIT 6

BIT 5

BIT 4

BIT 3

BIT 2

BIT 1

BIT 0

FUNCTION

00

DCOMP

SIGN

FTUNEH

Frequency Tuning High

01

FTUNEL

Frequency Tuning Low

02

SIGN

TREGH

Temperature MSB

03

TREGL

Temperature LSB

STOP

CONDITION

OR REPEATED

START

CONDITION

REPEATED IF MORE BYTES

ARE TRANSFERED

ACK

START

CONDITION

ACK

ACKNOWLEDGEMENT

SIGNAL FROM RECEIVER

ACKNOWLEDGEMENT

SIGNAL FROM RECEIVER

SLAVE ADDRESS

MSB

SCL

SDA

R/W

DIRECTION

BIT

12

6

7

8

9

1

2

8

9

3–7