Rockwell Automation 1775-KA PLC-3 Communication Adapter Module User Manual - Manual (Page 50)

Data Highway Communication
Chapter 3
3Ć5
When the rung becomes true, the message instruction begins sending
command(s) across the Data Highway. At the same time, bits in a control
file word change their state (Table 3.B) to reflect the status of the
command. Even if the rung becomes false, the message command will
continue to send commands across the highway.
Table 3.B
The Status of Bits in a Control File Word
WHEN:
the message instruction is true
the enable bit (16) is set
the latched enable bit (12) is set
the remote Data Highway module has received the message instruction
the request bit (17) is set
the 1775-KA module begins operation
the busy bit (14) is set
the operation is complete
the busy bit (14) is set
either the done bit (15) or the error bit (13) is set
the rung becomes false
the request bit (17) is reset
the busy bit (14) is reset
the enable bit (16) is reset
the latched enable bit (12) is reset
the rung becomes true a second time
either the done bit (15) or the error bit (13) is reset
5. Enter an extended address for the channel. In our Figure 3.1, we
address the module status area of memory, specify the 1775–KA
module, and a thumbwheel setting of 1.
6. Enter either a command or a command procedure. In Figure 3.1, we
entered the command procedure, PROC_A.
Data Highway Message Procedure
As already stated, the 1775–KA module has its own programming
language that consists of commands (Chapter 8). A group of related
commands make up a Data Highway message procedure. These
commands and message procedures determine what messages are
transmitted over the Data Highway.