Datasheet

MCP3550/1/3
DS20001950F-page 24  2005-2014 Microchip Technology Inc.
5.4.1 READY FUNCTION OF SDO/RDY
PIN IN CONTINUOUS CONVERSION
MODE
The device enters Continuous Conversion mode if no
rising edge of CS
is seen during t
CONV
and
consecutive conversions ensue. SDO/RDY
will be
high, indicating that a conversion is in process. When
a conversion is complete, SDO/RDY will change to a
Low state. With the Low state of SDO/RDY
after this
first conversion, the conversion data can be accessed
with the combination of SCK and SDO/RDY. If the data
ready event happens during the clocking out of the
data, the data ready bit will be displayed after the
complete 24-bit word communication (i.e., the data
ready event will not interrupt a data transfer).
If 24 bits of data are required from this conversion, they
must be accessed during this communication. You can
terminate data transition by bringing CS
high, but the
remaining data will be lost and the converter will go into
Shutdown mode. Once the data has been transmitted
by the converter, the SDO/RDY
pin will remain in the
LSB state until the 25th falling edge of SCK. At this
point, SDO/RDY is released from the Data Acquisition
mode and changed to the RDY
state.
5.4.2 2-WIRE CONTINUOUS
CONVERSION OPERATION,
(CS
TIED PERMANENTLY LOW)
It is possible to use only two wires to communicate with
the MCP3550/1/3 devices. In this state, the device is
always in Continuous Conversion mode, with internal
conversions continuously occurring. This mode can be
entered by having CS
low during power-up or changing
it to a low position after power-up. If CS
is low at power-
up, the first conversion of the converter is initiated
approximately 300 µs after the power supply has
stabilized.
Note: The RDY
state is not latched to CS in this
mode; the RDY flag dynamically updates
on the SDO/RDY pin and remains in this
state until data is clocked out using the
SCK pin.