Microchip Technology MCP3901EV-MCU16 Data Sheet

DS22192D-page 38

© 2011 Microchip Technology Inc.

To signify when channel data is ready for transmission,
the data ready signal is available on the Data Ready pin
(DR) through an active-low pulse at the end of a
channel conversion.

The data ready pin outputs an active-low pulse with a
period that is equal to the DRCLK clock period, and
with a width equal to one DMCLK period.

When not active-low, this pin can either be in high-
impedance (when DR_HIZN = 0) or in a defined logic
high state (when DR_HIZN = 1). This is controlled
through the Configuration registers. This allows
multiple devices to share the same data ready pin (with
a pull-up resistor connected between DR and DV

DD

) in

3-phase, energy meter designs to reduce pin count. A
single device on the bus does not require a pull-up
resistor.

After a data ready pulse has occurred, the ADC output
data can be read through SPI communication. Two sets
of latches at the output of the ADC prevent the
communication from outputting corrupted data (see

).

The CS pin has no effect on the DR pin, which means
even if CS is high, data ready pulses will be provided
(except when the configuration prevents them from
outputting data ready pulses). The DR pin can be used
as an interrupt when connected to an MCU or DSP.
While the RESET pin is low, the DR pin is not active.

To ensure that both channels’ ADC data is present at
the same time for SPI read, regardless of phase delay
settings for either or both channels, there are two sets
of latches in series with both the data ready and the
‘read start’ triggers.

The first set of latches holds each output when the data
is ready and latches both outputs together when
DRMODE<1:0> = 00. When this mode is on, both
ADCs work together and produce one set of available
data after each data ready pulse (that corresponds to
the lagging ADC data ready). The second set of latches
ensures that when reading starts on an ADC output, the
corresponding data is latched so that no data
corruption can occur.

If an ADC read has started, in order to read the
following ADC output, the current reading needs to be
completed (all bits must be read from the ADC Output
Data registers). 

6.10.1

DATA READY PIN (DR) CONTROL 
USING DRMODE BITS

There are four modes that control the data ready
pulses and these modes are set with the
DRMODE<1:0> bits in the STATUS/COM register. For
power metering applications, DRMODE<1:0> = 00 is
recommended (Default mode).