Watlow Series D8 - Manual (Page 73)

Series D8 User’s Guide Chapter 3: Communicating by DeviceNet
Doc. 0600-3120-2000 Watlow Anafaze 55
Figure 3.8 also shows the power level for loop 1 being scaled.
The scanned value is also in tenths, so 1000 means 100%
power (see Heat/Cool Output on page 122).
According to Figure 3.14 on page 65, M1:1.8 will hold the Set
Point for loop 1. This value is copied by the ladder logic to
N14:8. The 8 words after the set points, starting at M1:1.16
copied to N14:16 contain the Heat Output power for loops 1
to 8. Figure 3.9 shows the copied values for loop 1 to 8's Pro-
cess Variables and Set Points and the Heat Outputs for loops
1 to 4.
Figure 3.9 Contents of the PLC Memory
Setting a Value with an Explicit Message
The Allen-Bradley 1747-SDN scanner module provides ded-
icated memory for explicit messages. In this model M0:1.224
is the first of 32 words that may be used for an explicit mes-
sage (see Allen-Bradley Publication 1747-IN058C-EN-P -
May 2002).
In the first rung of ladder logic in Figure 3.10 on page 56
when the Enable Power Out Write (B17:0/6) is on, the PLC
writes to the scanner. At the first off-to-on transition of
B17:0/6 the copy instruction (COP) sends an explicit message
to the scanner. In this example, the message changes the Heat
Output for loop 1 to the value specified in N14:56.
NOTE! The Heat Output can only be set via De-
viceNet when the loop is in the Manual Mode.
If the loop's Mode is Off, Tune or Auto, the
controller sets the Heat Output.
The copy instruction in the second rung of logic is executed
only when a response to a previously sent explicit message is
available to be read and interpreted by the ladder program
(I:1/15). If communications is successful with the D8, the
copy instruction returns an echo of N14:50 and places it in
N14:60. If this echo occurs, the MVM instruction deletes the
transaction from the response queue. If communications is not
successful, an error code is returned via N14:60. For all error
code definitions, see the Allen-Bradley publication mentioned
above.