Watlow CLS200, MLS300 and CAS200 User Manual download pdf (Page 21)

Chapter 1: ANAFAZE/AB Protocol

Communications Speciﬁcation 15

Data for a Write Command

For a block write command, the block contains the bytes to write (up to

242 bytes of data). The controller sends back a message packet without

data.

Two-Byte Data Types

For two-byte data types, like process variable and setpoint, the

controller or host software sends the data in two-byte pairs with the least

signiﬁcant byte ﬁrst.

Figuring Block Size

In order to read parameter values, you must know how many bytes to

request. Parameter values are stored contiguously such that the setpoints

for all the loops are stored together and in loop number order. For

example, to read the deviation alarm deadband value for loops one to

ﬁve, you would read ﬁve bytes starting at x05A0. Some parameters,

such as setpoint, require two bytes of memory to store. So, for example,

if you want to read the setpoint for four loops, you must read eight

bytes.

Figure total block size in bytes for most loop parameters this way (do

not forget the pulse loop):

(Data Size) * (Number of Loops)

Some parameters have values for both heat and cool. Figure block size

for such a parameter this way:

2 * (Data Size) * (Number of Loops)

One exception is the units for each loop. Figure the data size for the

units this way:

3 * (Number of Loops)

Parameters that are not loop parameters (like system status, digital

inputs, or digital outputs) have speciﬁc data sizes. These data sizes are

listed in the data table in the next section.

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Watlow CLS200, MLS300 and CAS200 User Manual Page 21