390 Rockwell Automation Publication 1444-UM001D-EN-P - June 2018
Appendix A CIP Objects
0x4C CM Record Request
CM data is retrieved using a series of request/response unconnected messages.
One service is used to both start and continue with a session. The first request
initiates the session and subsequent requests return values that the service
returns. When the packet count down value that is returned reaches 0, the
session is completed.
The instance and attribute can be set to 1, but they are ignored.
The host sends the following CM Record Request Parameters as part of an
0x4C service request.
Table 118 - CM Record Request Parameters
Byte Offset Within
Structure
Structure Member Data Type Description
0 BufferSelect INT Specify the buffer to retrieve the data from:
• eHIGH_RES_TREND (0)
• eLOW_RES_TREND (1)
•eFFT (2)
•eTWF (3)
•eTACHO (4)
• eHIGH_RES_ALARM (5)
• eLOW_RES_ALARM (6)
•eFFT_ALARM (7)
•eTWF_ALARM (8)
• eTACHO_ALARM (9)
The BufferSelect does not change during a session.
2 RequestedCount UINT RequestedCount = 0 returns all records in the buffer.
RequestedCount = 1 returns the most recently collected record.
Any other positive count returns that number of records from the buffer. If the count is greater
than the max available records, the max available records are returned instead.
The RequestedCount does not change during a session.
4 SessionInstance USINT The SessionInstance is initially specified as 0, but on subsequent calls the SessionInstance
returned in CM Record Response must be passed here.
5 ChannelSelect BYTE 4 Bits indicating the source channel. The ChannelSelect does not change during a session (see
Channel Select).
This field is ignored for all overall buffer types (eHIGH_RES_TREND,
eLOW_RES_TREND, eHIGH_RES_ALARM, eLOW_RES_ALARM)
6 SpecialRequest BYTE See Table 119 on page 391
.
7 Pad BYTE Used to align data to a 32-bit boundary.
8 PacketCountDown DWORD The PacketCountDown is initially specified as 0, but on subsequent calls the PacketCountDown
returned in the CM Record Response must be passed here.
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