UCS81003 datasheet(96/108 Pages) MICROCHIP

96 / 108 page

UCS81003

DS20005334A-page 96

 2014 Microchip Technology Inc.

11.2.1

SYSTEM MANAGEMENT BUS

In SMBus mode, the UCS81003 communicates with a

host controller. The SMBus is a two-wire serial

communication protocol between a computer host and

its peripheral devices. A detailed timing diagram is

shown in Figure 11-1. Stretching of the SMCLK signal

is supported; however, the UCS81003 will not stretch

the clock signal.

FIGURE 11-1:

SMBus Timing Diagram.

11.2.1.1

SMBus Start Bit

The SMBus Start bit is defined as a transition of the

SMBus data line from a logic ‘1’ state to a logic ‘0’ state

while the SMBus clock line is in a logic ‘1’ state.

11.2.1.2

SMBus Address and RD/WR Bit

The SMBus Address Byte consists of the 7-bit client

address followed by the RD/WR indicator bit. If this

RD/WR bit is a logic ‘0’, the SMBus host is writing data

to the client device. If this RD/WR bit is a logic ‘1’, the

SMBus host is reading data from the client device.

The SMBus address is determined based on the resistor

connected on the SEL pin as shown in Table 11-2.

SMDATA

SMCLK

BUF

S - Start Condition

P - Stop Condition

THIGH

TLOW

HD:STA

SU:STO

HD:STA

HD:DAT

SU:DAT

SU:STA

FALL

RISE

Note:

If it is necessary to connect the SEL pin to

VDD via a resistor, the pull-up resistor may

be any value up to 100 k

.

TABLE 11-2:

SEL PIN DECODE

Resistor (±5%)

PWR_EN Polarity

SMBus Address

GND

Active Low

1010_111(r/w)

10 k

 pull-down

Active Low

1010_110(r/w)

12 k

 pull-down

Active Low

1010_101(r/w)

15 k

 pull-down

Active Low

1010_100(r/w)

18 k

 pull-down

Active Low

0110_000(r/w)

22 k

 pull-down

Active Low

0110_001(r/w)

27 k

 pull-down

Active Low

0110_010(r/w)

33 k

 pull-down

Active Low

0110_011(r/w)

47 k

 pull-down

Active High

0110_011(r/w)

56 k

 pull-down

Active High

0110_010(r/w)

68 k

 pull-down

Active High

0110_001(r/w)

82 k

 pull-down

Active High

0110_000(r/w)

100 k

 pull-down

Active High

1010_100(r/w)

120 k

 pull-down

Active High

1010_101(r/w)

150 k

 pull-down

Active High

1010_110(r/w)

VDD (If a pull-up resistor is used,

its value must not exceed 100 k

)

Active High

1010_111(r/w)

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