Datasheet

© 2008 Microchip Technology Inc. DS21298E-page 19
MCP3204/3208
5.0 SERIAL COMMUNICATIONS
Communication with the MCP3204/3208 devices is
accomplished using a standard SPI-compatible serial
interface. Initiating communication with either device is
done by bringing the CS
line low (see Figure 5-1). 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
IN
high will
constitute 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. The next
three bits (D0, D1 and D2) are used to select the input
channel configuration. Ta b l e 5 -1 and Tab l e 5- 2 show
the configuration bits for the MCP3204 and MCP3208,
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.
Once the D0 bit is input, one more clock is required to
complete the sample and hold period (D
IN
is a “don’t
care” for this clock). On the falling edge of the next
clock, the device will output a low null bit. The next 12
clocks will output the result of the conversion with MSB
first, as shown in Figure 5-1. Data is always output from
the device on the falling edge of the clock. If all 12 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 5-2. 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
IN
line before the start bit. This is
often done when dealing with microcontroller-based
SPI ports that must send 8 bits at a time. Refer to
Section 6.1 “Using the MCP3204/3208 with Micro-
controller (MCU) SPI Ports” for more details on using
the MCP3204/3208 devices with hardware SPI ports.
TABLE 5-1: CONFIGURATION BITS FOR
THE MCP3204
TABLE 5-2: CONFIGURATION BITS FOR
THE MCP3208
Control Bit
Selections
Input
Configuration
Channel
Selection
Single/
Diff
D2* D1 D0
1 X 0 0 single-ended CH0
1 X 0 1 single-ended CH1
1 X 1 0 single-ended CH2
1 X 1 1 single-ended CH3
0 X 0 0 differential CH0 = IN+
CH1 = IN-
0 X 0 1 differential CH0 = IN-
CH1 = IN+
0 X 1 0 differential CH2 = IN+
CH3 = IN-
0 X 1 1 differential CH2 = IN-
CH3 = IN+
* D2 is a “don’t care” for MCP3204
Control Bit
Selections
Input
Configuration
Channel
Selection
Single
/Diff
D2 D1 D0
1 0 0 0 single-ended CH0
1 0 0 1 single-ended CH1
1 0 1 0 single-ended CH2
1 0 1 1 single-ended CH3
1 1 0 0 single-ended CH4
1 1 0 1 single-ended CH5
1 1 1 0 single-ended CH6
1 1 1 1 single-ended CH7
0 0 0 0 differential CH0 = IN+
CH1 = IN-
0 0 0 1 differential CH0 = IN-
CH1 = IN+
0 0 1 0 differential CH2 = IN+
CH3 = IN-
0 0 1 1 differential CH2 = IN-
CH3 = IN+
0 1 0 0 differential CH4 = IN+
CH5 = IN-
0 1 0 1 differential CH4 = IN-
CH5 = IN+
0 1 1 0 differential CH6 = IN+
CH7 = IN-
0 1 1 1 differential CH6 = IN-
CH7 = IN+