Rockwell Automation 1404-M4_M5_M6_M8 Powermonitor 3000 User Manual, Firmware rev. 3.0 or LATER - Manual (Page 99)

Publication 1404-UM001F-EN-P - November 2009 99
Communication Chapter 4
Word 0 contains a transmit identifier (TXID) and command byte.
Assign each explicit message a unique TXID in the range of 0…255
decimal (0 to FF hex). The TXID is used to identify the response to
this message request. These are valid command codes:
•
1 hex = Execute transaction block. Use this command first to
start the explicit message.
•
4 hex = Delete transaction from response queue. Use this
command after you copy the response from the scanner to
remove the response from the scanner and enable further
explicit messages.
Word 1 contains the DeviceNet scanner port number and the
transaction body size in bytes. The SLC 500 scanner module uses only
port 0; a PLC-5 DeviceNet scanner module has two ports, 0 and 1. For
a read request, the transaction body size is 3 words, therefore 6 bytes.
See the Explicit Messaging table on page 98 for more information.
For a write, the body size is the data size in bytes plus the 6-byte path
(class/instance/attribute).
Word 2 contains the DeviceNet service code and the MAC ID or node
number of the server device, in this case, the power monitor. Valid
service codes for use on Class 4 assembly instances include the
following:
•
0E hesx (14 decimal) = Get_Attribute_Single. Requests a read of
the entire assembly instance defined in the transaction body.
•
10 hex (16 decimal) = Set_Attribute_Single. Writes the data
contained in the message to the assembly instance defined in
the transaction body.
Words 3…5 comprise the DeviceNet path: Class, Instance, and
Attribute. For the power monitor data tables, Class = 4, Assembly
Objects; Attribute identifies the data table, and Attribute = 3, data.
Word 6 and following words contain data to write to the power
monitor.
TIP
A convenient way to build Words 0, 1, and 2 is to multiply the high
byte value by 256 and add the low byte value, using decimal values
for each parameter. Example: TXID = 121; Command = 1. Word 0 =
121*256 + 1 = 30977.