Watlow CLS200, MLS300 and CAS200 - Manual (Page 63)

Chapter 3: Controller Parameter Descriptions
Communications Specification 57
Data Changed Register (32)
The data changed register acts as a First-In-First-Out (FIFO) to point to
parameters that have changed internally. The host software must query
this register after receiving a “Data Changed” status flag to determine
which data has changed. (For more information about “Data Changed”
status flags, see the Status Byte section in Chapter 1.)
• Range: 0 to 255.
The general program flow goes like this:
(1) If there is anything in the controller’s internal Data Changed Stack,
the controller returns a “Data Changed” status flag. (See the Status
Byte section in Chapter 1 for an explanation of the “Data Changed”
status flag.)
(2) The host receives a “Data Changed” flag in the communications
packet.
(3) The host reads the Data Changed Register for the command number
of the parameter that changed and then uploads that data block.
(4) The controller notes that the Data Changed Register has been read
and waits for an Acknowledge from the host. When the Acknowl-
edge has been received, the controller checks its own Data Changed
Stack. If there are still data blocks that have been changed, but not
uploaded, the controller puts the next command number in the Data
Changed Register and continues to return a “Data Changed” status
in communications packets. Otherwise, the Data Changed Register
is cleared and no more Data Changed status flags are returned. (For
more help on this topic, see the Status Byte section in Chapter 1.)
Input Units (33)
MLS, CLS, and CAS show the process variable expressed in
engineering units. This parameter consists of three character strings that
provide text representation of the engineering units for each loop. (The
default input units for a J-type thermocouple—the default input type—
are in °F.)
For thermocouple and RTD inputs, the input units are preset; the third
character of the loop’s string indicates whether the reading is in degrees
Celsius (if the second and third characters are “°C”), or in degrees
Fahrenheit (if the second and third characters are “°F”).
5 * Manufacturing Test
6 Parameter reset bit
7 Reserved
* Warning: This may cause loss of data when used in normal
operation. Use only when these tests are absolutely necessary.
Bit 0 1