DA6501.001

27 October 2008

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I

I2C Bus Protocol Definitions

Two wire I2C bus protocol has special bus signal

conditions. Figure 2 shows start (S), stop (P) and

binary data conditions. At start condition the SCL is

high and SDA has falling edge. At stop condition the

SCL is also high but SDA has rising edge. Data

must be held stable in SDA pin when SCL is high.

Data can change value at SDA pin only when SCL is

low.

SDA

SCL

S

P

1

0

Figure 2. I2C protocol definitions

I2C

contains

also

acknowledge

(A)

and

not

acknowledge (N) commands. At acknowledge the

master device sends 0 bit to SDA bus (pulls down

SDA) for one SCL clock cycle. At not acknowledge

(N) the slave device sends 0 bit to SDA (pulls down

SDA) for one SCL clock cycle.

Abbreviations:

A= Acknowledge by Slave

N = Not Acknowledge by Master

S = Start

P = Stop

Conversion Starting – Write Sequence

Conversion is started by first writing measurement

configuration bits into the control register. Write

sequence is illustrated in Table 4.

To start conversion the control register SCO bit has

to be set high (SCO=1, see control register bit

description in table 1).

Table 4. MAS6501 I2C bus write sequence bits

S

AW

A

AC

A

DC

A

P

Abbreviations:

AW = Device Write Address (%1110 1110)

AR = Device Read Address (%1110 1111)

AC = Control Register Address (%1111 1111)

Ax = MSB (x=M, %1111 1101) or LSB (x=L, %1111

1110) ADC Result Register Address

DC = Control Register Data

Dx = MSB (x=M) or LSB (x=L) A/D Result Register

Data

Each I2C bus operation like write starts with start

command (see figure 2). After start the MAS6501

device address with write bit (AW, see table 2) is

sent and ended to acknowledge (A). After this

control register address (AC, see table 3) is sent

and ended to acknowledge (A). Next control register

data (DC, see table 1) is written and ended to

acknowledge (A). Finally the I2C bus operation is

ended with stop command (see figure 2).

A/D Conversion

A/D conversion is progressed by running MCLK

signal

until

EOC

goes

high

indicating

that

conversion is done and data is ready for reading.