MC74

http://onsemi.com

7

REGISTER SET and PROGRAMMER’S MODEL

MC74 Command Set

(SMBus READ_BYTE and WRITE_BYTE)

Command Byte Description

Command

Code

Function

RTR

00h

Read Temperature (TEMP)

RWCR

01h

Read/Write Configuration (CONFIG)

Configuration Register (CONFIG), 8–BITS,

READ/WRITE

Configuration Register (Config)

D[7]

D[6]

D[5]

D[4]

D[3]

D[2]

D[1]

D[0]

SHDN

Data Rdy

Reserved

Bit

POR

Function

Type

Operation

D[7]

0

STANDBY switch

Read/

Write

1 = standby,

0 = normal

D[6]

0

Data Ready*

Read

Only

1 = ready,

0 = not ready

D[5]—D[0]

0

Reserved — Al-

ways returns zero

when read.

N/A

N/A

*DATA_RDY bit reset at power–up and SHDN enable (see below).

Figure 3. . DATA_RDY, SHDN Operation Logic

Diagram

V

DD

t conv

t conv

DATA_RDY

SHDN

Temperature Register (TEMP), 8–Bits,

READ–ONLY

The binary value (2’s complement format) in this register

represents temperature of the integrated sensor following a

conversion cycle. The registers are automatically updated in

an alternating manner.

Temperature Register (TEMP)

D[7]

D[6]

D[5]

D[4]

D[3]

D[2]

D[1]

D[0]

MSB

x

x

x

x

x

x

LSB

In the temperature data registers, each unit value

represents one degree (Celsius).

The value is in

2’s–complement binary format such that a reading of 0000

0000b corresponds to 0

°C. Examples of this temperature to

binary value relationship are shown in the following table.

Temperature–to–Digital Value Conversion (TEMP)

ACTUAL

TEMPERATURE

REGISTERED

TEMPERATURE

BINARY HEX

+130.00

°C

+127

°C

0111 1111

+127.00

°C

+127

°C

0111 1111

+126.50

°C

+127

°C

0111 1111

+25.25

°C

+25

°C

0001 1001

+0.50

°C

+1

°C

0000 0001

+0.25

°C

0

°C

0000 0000

0.00

°C

0

°C

0000 0000

-0.25

°C

0

°C

0000 0000

-0.50

°C

0

°C

0000 0000

-0.75

°C

-1

°C

1111 1111

-1.00

°C

-1

°C

1111 1111

-25.00

°C

-25

°C

1110 0111

-25.25

°C

-25

°C

1110 0110

-54.75

°C

-55

°C

1100 1001

-55.00

°C

-55

°C

1100 1001

-65.00

°C

-65

°C

1011 1111

Register Set Summary

The MC74’s register set is summarized below. All

registers are 8–bits wide.

Name

Description

POR State

Read

Write

TEMP

Internal sensor

temperature (2’s

complement)

0000 0000b*

√

CONFIG

CONFIG register

0000 0000b

√

√

*NOTE: The TEMP register immediately will be updated by the

A/D converter after the DATA_RDY bit goes high.