MCP3304 Microchip Technology, MCP3304 Datasheet - Page 23

• Manufacturer Part Number: MCP3304
• Description: 13-Bit Differential Input, Low Power A/D Converter with SPI Serial Interface
• Manufacturer: Microchip Technology

7.2
Communication with the MCP3302/04 devices is done
using a standard SPI-compatible serial interface. Initi-
ating communication with either device is done by
bringing the CS line low (see Figure 7-2). If the device
was powered up with the CS pin low, it must be brought
high and back low to initiate communication. The first
clock received with CS low and D
a start bit. The SGL/DIFF bit follows the start bit and will
determine if the conversion will be done using single
ended or differential input mode. Each channel in
single ended mode will operate as a 12-bit converter
with a unipolar output. No negative codes will be output
in single ended mode. The next three bits (D0, D1 and
D2) are used to select the input channel configuration.
Table 7-2 and Table 7-3 show the configuration bits for
the MCP3302 and MCP3304, respectively. The device
will begin to sample the analog input on the fourth rising
edge of the clock after the start bit has been received.
The sample period will end on the falling edge of the
fifth clock following the start bit.
After the D0 bit is input, one more clock is required to
complete the sample and hold period (D
care” for this clock). On the falling edge of the next
clock, the device will output a low null bit. The next 13
clocks will output the result of the conversion with the
sign bit first, followed by the 12 remaining data bits, as
shown in Figure 7-2. Note that if the device is operating
in the single ended mode, the sign bit will always be
transmitted as a ‘0’. Data is always output from the
device on the falling edge of the clock. If all 13 data bits
have been transmitted, and the device continues to
receive clocks while the CS is held low, the device will
output the conversion result, LSB, first, as shown in
Figure 7-3. If more clocks are provided to the device
while CS is still low (after the LSB first data has been
transmitted), the device will clock out zeros indefinitely.
If necessary, it is possible to bring CS low and clock in
leading zeros on the D
often done when dealing with microcontroller-based
SPI ports that must send 8 bits at a time. Refer to
Section 7.3 for more details on using the MCP3302/04
devices with hardware SPI ports
© 2007 Microchip Technology Inc.
Communicating with the MCP3302
and MCP3304
IN
line before the start bit. This is
IN
high will constitute
IN
is a “don’t
TABLE 7-2:
TABLE 7-3:
*D2 is don’t care for MCP3302
Single
SinglE
/Diff
/Diff
1
1
1
1
0
0
0
0
1
1
1
1
1
1
1
1
0
0
0
0
0
0
0
0
Control Bit
Control Bit
Selections
Selections
D2* D1 D0
D2
X
X
X
X
X
X
X
X
0
0
0
0
1
1
1
1
0
0
0
0
1
1
1
1
D1 D0
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
1
CONFIGURATION BITS FOR
THE MCP3302
CONFIGURATION BITS FOR
THE MCP3304
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
MCP3302/04
Configuration
Configuration
single ended
single ended
single ended
single ended
single ended
single ended
single ended
single ended
single ended
single ended
single ended
single ended
differential
differential
differential
differential
differential
differential
differential
differential
differential
differential
differential
differential
Input
Input
DS21697C-page 23
CH0 = IN+
CH1 = IN+
CH2 = IN+
CH3 = IN+
CH4 = IN+
CH5 = IN+
CH6 = IN+
CH7 = IN+
CH1 = IN-
CH0 = IN-
CH3 = IN-
CH2 = IN-
CH5 = IN-
CH4 = IN-
CH7 = IN-
CH6 = IN-
CH0 = IN+
CH1 = IN+
CH2 = IN+
CH3 = IN+
Selection
CH1 = IN-
CH0 = IN-
CH3 = IN-
CH2 = IN-
Selection
Channel
Channel
CH0
CH1
CH2
CH3
CH4
CH5
CH6
CH7
CH0
CH1
CH2
CH3