Rainbow-electronics MAX6871 Manual de usuario descargar pdf (Pagina 34)

MAX6870/MAX6871

EEPROM-Programmable Hex/Quad

Power-Supply Sequencers/Supervisors with ADC

34 ______________________________________________________________________________________

and the master device at clock rates up to 400kHz. Figure

2 shows the interface timing diagram. The

MAX6870/MAX6871 are transmit/receive slave-only

devices, relying upon a master device to generate a

clock signal. The master device (typically a microcon-

troller) initiates data transfer on the bus and generates

SCL to permit that transfer.

A master device communicates to the MAX6870/

MAX6871 by transmitting the proper address followed by

command and/or data words. Each transmit sequence is

framed by a START (S) or REPEATED START (SR) condi-

tion and a STOP (P) condition. Each word transmitted

over the bus is 8 bits long and is always followed by an

acknowledge pulse.

SCL is a logic input, while SDA is a logic input/open-

drain output. SCL and SDA both require external pullup

resistors to generate the logic-high voltage. Use 4.7kΩ

for most applications.

Bit Transfer

Each clock pulse transfers one data bit. The data on

SDA must remain stable while SCL is high (Figure 3),

otherwise the MAX6870/MAX6871 register a START or

STOP condition (Figure 4) from the master. SDA and

SCL idle high when the bus is not busy.

Start and Stop Conditions

Both SCL and SDA idle high when the bus is not busy. A

master device signals the beginning of a transmission

with a START (S) condition (Figure 4) by transitioning

SDA from high to low while SCL is high. The master

device issues a STOP (P) condition (Figure 4) by transi-

tioning SDA from low to high while SCL is high. A STOP

STOP

CONDITION

REPEATED START

CONDITION

START

CONDITION

HIGH

LOW

SU:DAT

SU:STA

SU:STO

HD:STA

BUF

HD:STA

HD:DAT

SCL

SDA

START

CONDITION

Figure 2. Serial-Interface Timing Details

DATA LINE STABLE,

DATA VALID

SDA

SCL

CHANGE OF

DATA ALLOWED

Figure 3. Bit Transfer

START

CONDITION

SDA

SCL

STOP

CONDITION

Figure 4. Start and Stop Conditions

1 2 ... 29 30 31 32 33 34 35 36 37 38 39 ... 50 51

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Rainbow-electronics MAX6871 Manual de usuario Pagina 34

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