DA6501.001
27 October 2008
I2C SERIAL INTERFACE CONTROL...
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.
S
P
1
0
SDA
SCL
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
DC
S
AW
A
AC
A
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.
7 (16)
MAS [ MICRO ANALOG SYSTEMS ]
