Watlow CLS200, MLS300 and CAS200 - Manual (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.