Rockwell Automation 1747-PT1, D1747NP002 Hand-Held Terminal - Manual (Page 260)

Instructions
Chapter 18
I/O Message and Communication
18–14
SLC 5/02 Processors Only
Service Communications SVC Output Instruction
(SVC)
(SVC)
F1 F2 F3 F4 F5
ZOOM on SVC –(SVC)– 2.0.0.0.1
NAME: SERVICE COMMUNICATIONS
EDT_DAT
HHT Ladder Display:
HHT Zoom Display:
Ladder Diagrams and APS Displays:
(monitor mode)
The SVC instruction has no programming parameters. When it is evaluated
as true, the program scan is interrupted to execute the service
communications part of the operating cycle. The scan then resumes at the
instruction following the SVC instruction.
An explanation of the processor operating cycle appears in appendix D.
One status file bit is related to the SVC instruction:
•
Bit S:2/5 DH–485 Incoming Command Pending – Read only. This bit
becomes set when the processor determines that another node on the
DH–485 network has requested information or supplied a command to it.
This bit can become set at any time. This bit is cleared when the
processor services the request (or command).
Use this bit as a condition of an SVC instruction to enhance the
communications capability of your processor.
You are not allowed to place an SVC instruction in an STI interrupt, I/O
interrupt, or user fault subroutine.
Application example: The SVC instruction is used when you want to
execute a communications function, such as transmitting a message, prior to
the normal service communications portion of the operating scan:
] [
S:2
7
(SVC)
Outgoing Message
Command Pending Bit
You can place this rung after a message instruction. S:2/7 will be set when
the message instruction is enabled and waiting (provided no message is
currently being transmitted). When S:2/7 is set, the SVC instruction is
evaluated as true and the program scan is interrupted to execute the service
communications portion of the operating scan. The scan then resumes at the
instruction following the SVC instruction.
Service Communications
(SVC)