Rockwell Automation 1770, D17706.5.16 Ref Mnl DF1 Protocol Command - Manual (Page 28)

1–11 Network Layers
Publication 1770Ć6.5.16 - October 1996
Types of Commands
From your computer on a DF1 link to a node on a DH, DH+ or
DH485 link, you can send four types of commands:
•
read
•
write
•
diagnostic
•
upload/download
For additional information on the commands you can send,
see Chapter 7, “Communication Commands.”
Error Codes
When your computer sends a command on the asynchronous link, a
status code is returned in the reply message. This code tells you the
status of the command sent from your computer. You must program
your computer to interpret this code. For more information on codes
and their meanings, see Chapter 8, “Message Packet Status Codes.”
Error codes can be generated at two places:
•
the sending node
•
the receiving node
For codes that are returned from the sending node:
From this node Error codes are generated when
sending node
• an application program used the wrong message format or issued
illegal commands.
• the sending node cannot complete a transaction due to network
problems.
receiving node
an application problem exists at the receiving node. Typically, these
involve:
• the PLC processor being off line (in Program mode, for example)
or
• the command trying to access a memory area is blocked by the
interface module or user application program (i.e., the data table
location does not exist or is restricted).