Watlow CLS200, MLS300 and CAS200 User Manual download pdf (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

1 2 ... 58 59 60 61 62 63 64 65 66 67 68 ... 91 92

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Watlow CLS200, MLS300 and CAS200 User Manual Page 63

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