DA6502.008
29 November 2012
SERIAL DATA INTERFACE (I2C BUS) CONTROL
Conversion Starting – Write Sequence
Conversion is started by writing configuration bits
into the ADC control register. The write sequence is
illustrated in Table 8.
Table 8. MAS6502 I2C bus write sequence
S
AW
A
AC
A
DC
A
P
Abbreviations:
AW = Device Write Address (%1110 1110)
AR = Device Read Address (%1110 1111)
AC = ADC Control Register Address (%1111 1111)
Ax = MSB (x=M, %1111 1101) or LSB (x=L, %1111
1110) ADC Result Register Address
DC = ADC Control Register Data
Dx = MSB (x=M) or LSB (x=L) ADC Result Register
Data
Each serial bus operation, like write, starts with the
start (S) bit (see figure 3). After start (S) the
MAS6502 device address with write bit (AW, see
table 7) is sent followed by an Acknowledge (A).
After this the ADC control register address (see
table 1) is sent and followed by an Acknowledge
(A). Next the ADC control register data (DC, see
table 2) is written and followed by an Acknowledge
(A). Finally the serial bus operation is ended with a
stop (P) command (see figure 3).
A/D Conversion
After power-on-reset or external reset (XCLR) the
EOC output is high. After an A/D conversion is
started the EOC output is set low until the
conversion is finished and the EOC goes back high,
indicating that the conversion is done and data is
ready for reading. The EOC is set low only by
starting a new conversion. To save power the
internal oscillator runs only during conversion.
Conversion Result – Read Sequence
During the A/D conversion period the input signal is
sampled continuously leading to an output
conversion result that is a weighted average of the
samples taken. Note: The device should not be
addressed via serial bus before the conversion has
ended. Reading or writing to the device during the
conversion may corrupt the conversion result.
Table 9 shows a general control sequence for a
single register data read.
Table 9. MAS6502 I2C bus single register (address Ax) read sequence
AW Ax Sr AR Dx
S
A
A
A
N
P
Table 10 shows the control sequence for reading
the 16-bit A/D conversion result from both the MSB
and LSB data registers. The LSB register data (DL)
can be read right after the MSB register data (DM)
in case the read sequence is continued (not ended
by a Stop bit P) since the register address is
automatically incremented to point to the next
register address (in this case to point to the LSB
data register).
Table 10. MAS6502 I2C bus MSB (first) and LSB (second) A/D conversion result read sequence
AW AM Sr AR DM DL
S
A
A
A
A
N
P
12 (20)
MAS [ MICRO ANALOG SYSTEMS ]
