MCP3221 Microchip Technology, MCP3221 Datasheet - Page 17

• Manufacturer Part Number: MCP3221
• Description: Low Power 12-Bit A/D Converter With I2C Interface
• Manufacturer: Microchip Technology

The input signal will initially be sampled with the first
falling edge of the clock following the transmission of a
logic-high R/W bit. Additionally, with the rising edge of
the SCL, the ADC will transmit an acknowledge bit
(ACK = 0). The master must release the data bus dur-
ing this clock pulse to allow the MCP3221 to pull the
line low (refer to Figure 5-3).
For consecutive samples, sampling begins on the fall-
ing edge of the LSB of the conversion result, which is
two bytes long. Refer to Figure 5-6 a for timing diagram.
FIGURE 5-5:
5.3.3
For consecutive samples, sampling begins on the fall-
ing edge of the LSB of the conversion result. See
Figure 5-6 for timing.
FIGURE 5-6:
2003 Microchip Technology Inc.
SDA
SCL
SDA
SCL
CONSECUTIVE CONVERSIONS
S
T
A
R
T
S
S
T
A
R
T
S
1
1
Device bits
1
1
Device bits
2
0
Executing a Conversion.
Continuous Conversion.
0
2
t
initiated here
ACQ
3
0
Address Byte
t
initiated here
ACQ
3
0
Address Byte
+ t
4
1
+ t
CONV
4
Address bits
1 A2 A1 A0
5
A
2
CONV
Address bits
5
is
6
A
1
is
6
A
7
0
7
W
8
R
/
W
R
8
/
9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27
A
C
K
9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27
A
C
K
0
0
0
0
Upper Data Byte
Upper Data Byte (n)
0
0
0
0
f
11 10
SAMP
D
11 10 9
D
5.3.2
Once the MCP3221 acknowledges the address byte,
the device will transmit four ‘0’ bits followed by the upper
four data bits of the conversion. The master device will
then acknowledge this byte with an ACK = Low. With the
following 8 clock pulses, the MCP3221 will transmit the
lower eight data bits from the conversion. The master
then sends an ACK = high, indicating to the MCP3221
that no more data is requested. The master can then
send a stop bit to end the transmission.
D
= 22.3 ksps (f
D
D
9
D
D
8
D
8
A
C
K
READING THE CONVERSION DATA
CLK
A
C
K
D
7
= 400 kHz)
D
7
D
6
D
6
Lower Data Byte
Lower Data Byte (n)
D
5
t
initiated here
ACQ
D
5
D
4
+ t
D
4
D
3
CONV
D
3
MCP3221
D
2
is
D
2
D
1
D
1
DS21732B-page 17
D
0
D
0
N
A
K
A
C
K
P
S
T
O
P
28
0