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CMC TECHNICAL REFERENCE MANUAL
1X36003 Version 2.52
1996-1999 Ingersoll-Rand Company
Date of Issue: 18-Oct-1999
111
Source (SRC) Byte
This byte indicates the source node address of the message. If the command is initiated
from an Allen-Bradley PLC, the SRC byte will be the address of the processor module.
Command (CMD) and Function (FNC) Bytes
The CMD byte defines the command type. The FNC byte defines the specific function under
that command type. These bytes together define the activity being performed by the
command message at the destination node. The message format depends on the CMD and
FNC values.
CMD Byte
Bit:
7
6
5
4
3 2 1 0
0
0:Command msg
1:Reply msg
0: normal priority(for DH+)
1: high priority(only applies to DH link)
0
Command code
From the figure above, the CMD byte of a reply message for DH+ network is always 40h
ORed with the CMD byte of its original command message.
Status (STS) Byte - Status Error Code
Bit:
7
6
5
4
3
2
1
0
Remote Error Nibble
Local Error Nibble
Bits 7, 6, 5, and 4 are used to report remote errors - errors that occur when the command
executor at the destination node tries to execute the command message. Bits 3, 2, 1, and 0
are used to report local errors - errors found by the local source node and code 09h through
0Fh are not used. The UCM-DF1 driver uses mainly the higher nibble to report errors occur
in CMC. A special error code with non-zero local error nibble, 3Fh, is used to report errors
caused by illegal CMC data table address or count. The maximum number of data table
entries allowed to be read or set for CMC is 16 currently. If a read command requests more
than 16 data items from CMC, an exception response of 3Fh will be returned.
Following is a list of status error code supported by the UCM-DF1 driver:
Transaction (TNS) Bytes
The two TNS bytes contain a unique 16-bit transaction identifier. Generate this number by
maintaining a 16-bit counter. Increment the counter each time your command initiator
creates a new message, and store the counter value in the two TNS bytes of the new
message. You must use only one TNS counter in a multi-tasking environment.
If the command initiator is an Allen-Bradley PLC, the PLC will maintain the counter internally.
The reply message should have the same TNS value as the original command message.
The UCM-DF1 driver copies the original TNS field of the command message into the TNS
field of the corresponding reply message.
BCC (Block Check Character) and CRC (Cyclic Redundancy Check)
At the end of each DF1 command message, there is a one-byte BCC field, or a two-byte
CRC field for error checking. These bytes allow you to verify the accuracy of each message
frame transmission. SW-1 of 1770-KF2 module allows you to select BCC or CRC error