User Manual
Appendix B
GFK-1742F
Jan 2020
DSM314 Communications Request Instructions
398
loaded via a Word-type MOVE instruction, and the remaining decimal values are
loaded via Integer-type MOVEs.
B-3
The User Data Table (UDT) COMM REQ
The DSM314 has an 8192-byte memory area called the User Data Table (UDT) that is
designated for use with Local Logic (LL) programs. LL Programs can access all or part of this
memory to store and retrieve data. The UDT is useful for storing and retrieving large
amounts of data such as large batches of setup data.
The host controller CPU can write to or read from the UDT via a User Data Table
Communications Request (UDT COMM REQ) instruction in the host controller ladder
program. A single UDT COMM REQ reads or writes 2048 bytes of memory at a time.
Therefore, the UDT is logically divided into four 2048-byte segments, called Segments 1-4,
that can be accessed individually by a UDT COMM REQ. There is a unique Read and a unique
Write command for each of the four Segments, for a total of 8 possible UDT COMM REQ
commands.
B-3.1
User Data Table COMM REQ Features and Usage
Information
•
Reads or Writes 2K (2048) bytes at a time to the Local Logic User Data Table. No
other value is permitted.
•
Only works with the DSM314 module (will not work with the DSM302)
•
Cannot be used to download parameter data to the DSM314
•
This instruction adds about 15 ms to host controller scan (sweep) time for one scan
if the host controller’s Communication Window Sweep Control parameter is set to
COMPLETE (Run to Completion). If the Communication Window Sweep Control
parameter is set to LIMITED, the COMM REQ will be executed over several scans, with
a smaller impact on scan time. However, the COMM REQ probably will not be
executed repeatedly
–
it will only be executed when there is a need to change data.
Therefore, if it was sent on the First Scan, or during a job setup, it would not have an
impact while the application is running.
•
To avoid memory access conflicts, it is recommended that a Periodic Subroutine not
be used during the time this COMM REQ is active.
•
This COMM REQ does not support discrete memory for its host controller Data Type.