Datasheet
MCP3903
DS25048B-page 32 © 2011 Microchip Technology Inc.
FIGURE 6-5: Device Write (SPI Mode 1,1 - Clock Idles High).
6.7 Read Continuously Channel Data,
LOOPING ON ADDRESS SETS
If the user wishes to read back any of the ADC
channels continuously, or all channels continuously,
the internal address counter of the MCP3903 can be
set to loop on specific register sets. In this case, there
is only one control byte on SDI to start the
communication. The part stays within the same loop
until CS
returns high.
This internal address counter allows the following
functionality:
• Read one ADC channel data continuously
• Read all ADC channel data continuously (all ADC
data can be independent or linked with
DRn_MODE settings)
• Read continuously the entire register map
• Read continuously each separate register
• Read continuously all configuration registers
• Write all configuration registers in one
communication (see Figure 6-6)
The STATUS/COM register contains the loop settings
for the internal address counter (READ<1:0>). The
internal address counter can either stay constant
(READ<1:0>=00) and continuously read the same
byte, or it can auto-increment and loop through the
register groups defined below (READ<1:0>=01),
register types (READ<1:0>=10) or the entire register
map (READ<1:0>=11).
Each channel is configured independently as either a
16-bit or 24-bit data word, depending on the setting of
the corresponding WIDTH bit in the CONFIG register.
For continuous reading, in the case of WIDTH=0
(16-bit), the lower byte of the ADC data is not accessed
and the part jumps automatically to the following
address (the user does not have to clock out the lower
byte since it becomes undefined for WIDTH=0).
The following figure represents a typical continuous
read communication with the default settings
(DRMODE<1:0>=00, READ<1:0>=10) for both
WIDTH settings. This configuration is typically used for
power metering applications.
FIGURE 6-6: Typical Continuous Read Communication.
SCK
SDI
SDO
CS
R/W
A6
A5
A4
A3
A2
A1
A0
23 22
21
20
19
18
17
(ADDRESS) DATA
D6
D5
D4
D3
D2
D1
D16
DATA TRANSITIONS ON
THE FALLING EDGE
MCU AND MCP3901 LATCH
BITS ON THE RISING EDGE
D0
HI-Z
HI-Z
D7
HI-Z
D08
1
32
5CH5
CH55
CH5
CH5