MIC281
Micrel
Functional Description
Serial Port Operation
The MIC281 uses standard SMBus Write_Byte and Read_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_Byte operation is a composite write and read operation:
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. The command byte values corresponding to the various
MIC281 registers are shown in Table 1. Other command byte
values are reserved, and should not be used.
MIC281 Slave Address
DATA
CLK
Command Byte
Data Byte to MIC281
S 1 0 0 1
A2 A1 A0
0 A X X X X X X X X A
D7 D6 D5 D4 D3 D2 D1 D0
/A P
START
R/W = WRITE
ACKNOWLEDGE
ACKNOWLEDGE
NOT ACKNOWLEDGE
STOP
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
MIC281 Slave Address
DATA
CLK
Master to slave transfer,
i.e., DATA driven by master.
Slave to master transfer,
i.e., DATA driven by slave.
Command Byte
MIC281 Slave Address
Data Read From MIC281
S 1 0 0 1 X X X 0 A X X X X X X X X A S 1 0 0 1 X X X 1 A
X X X X X X X X
/A P
START
R/W = WRITE
ACKNOWLEDGE
ACKNOWLEDGE
START
R/W = READ
ACKNOWLEDGE
NOT ACKNOWLEDGE
STOP
Figure 2. Read_Byte Protocol
Target Register
Label
TEMP
CONFIG
MFG_ID
DEV_ID
Description
Remote temperature result
Configuration
Manufacturer identification
Device and revision identification
Command Byte
Value
Read
01
h
FE
h
FF
h
03
h
Write
n/a
03
h
n/a
n/a
Power-on
Default
00
h
(0°C)
2A
h
80
h
0x
h
*
* The lower nibble contains the die revision level, e.g., Rev 0 = 00h.
Table 1. MIC281 Register Addresses
MIC281
6
November 2004
MICREL [ MICREL SEMICONDUCTOR ]
