MIC281

Micrel

MIC281

6

November 2004

Functional Description

Serial Port Operation

TheMIC281usesstandardSMBusWrite_ByteandRead_Byte

operations for communication with its host. The SMBus

Write_Byte operation involves sending the device’s slave

address (with the R/W bit low to signal a write operation),

followed by a command byte and the data byte. The SMBus

Read_Byteoperationisacompositewriteandreadoperation:

the host first sends the device’s slave address followed by

the command byte, as in a write operation. A new start bit

must then be sent to the MIC281, followed by a repeat of the

slave address with the R/W bit (LSB) set to the high (read)

state. The data to be read from the part may then be clocked

out. These protocols are shown in Figures 1 and 2.

The Command byte is eight bits (one byte) wide. This byte

carries the address of the MIC281 register to be operated

upon.Thecommandbytevaluescorrespondingtothevarious

MIC281 registers are shown in Table 1. Other command byte

values are reserved, and should not be used.

S 1 0 0 1 A2 A1 A0 0 A X X X X X X X X A

D4

D5

D6

D3 D2 D1 D0

D7

/A P

MIC281 Slave Address

DATA

CLK

Command Byte

Data Byte to MIC281

START

STOP

R/W = WRITE

ACKNOWLEDGE

ACKNOWLEDGE

NOT ACKNOWLEDGE

Master to slave transfer,

i.e., DATA driven by master.

Slave to master transfer,

i.e., DATA driven by slave.

Figure 1. Write_Byte Protocol

S 1 0 0 1 X X X

X X X

0 A X X X X X X X X A S 1

1

1

0 0

X

X

X

X X X X

A X

/A P

MIC281 Slave Address

DATA

CLK

Command Byte

MIC281 Slave Address

Data Read From MIC281

START

START

STOP

R/W = WRITE

R/W = READ

ACKNOWLEDGE

ACKNOWLEDGE

ACKNOWLEDGE

NOT ACKNOWLEDGE

Master to slave transfer,

i.e., DATA driven by master.

Slave to master transfer,

i.e., DATA driven by slave.

Figure 2. Read_Byte Protocol

Command Byte

Power-on

Target Register

Value

Default

Label

Description

Read

Write

TEMP

Remote temperature result

n/a

CONFIG

Configuration

MFG_ID

Manufacturer identification

n/a

DEV_ID

Device and revision identification

n/a

* The lower nibble contains the die revision level, e.g., Rev 0 = 00h.

Table 1. MIC281 Register Addresses