Rockwell Automation T8xxx Trusted Communications Interface - Manual (Page 62)

Trusted
TM
Communication Interface T8151B
Issue 21 Apr 10 PD-T8151B 62
SEQ_NO is a read-only register maintained by the SOE Over Modbus service. Upon the start of the
service or after each acknowledged transfer, it is incremented when new event data is available.
NUM_BLKS is a read-only register maintained by the SOE Over Modbus service. When the SEQ_NO
field is incremented, the NUM_BLKS field will be updated to indicate the number of data blocks that are
available.
ACK_SEQ is a read/write register maintained by the Modbus master. When the Modbus master
completes reading the data for a given sequence, this field is update with that number. This informs
the SOE Over Modbus service that the Modbus master has finished reading the data for the specified
sequence.
ACK_BLKS is a read/write register is maintained by the Modbus master. When the Modbus master
completes reading the data for a given sequence and has acknowledged the sequence by writing to
the ACK_SEQ field, this field is updated with the number of data blocks read. It should always be the
same at the number of events specified in the NUM_BLKS field for the given sequence.
The SYNC registers are for the exclusive use of the SOE Over Modbus service. They contain the
internal event number of the last event read by the Modbus master. The SOE Over Modbus service
uses this information to synchronize the presentation of event data in a redundant, fail-over
configuration to prevent duplicate events when a fail-over occurs.
LEN_SOE is a read-only register maintained by the SOE Over Modbus service. It contains the number
of registers allocated as event data blocks. Note that this number specifies the number or registers,
not the number of blocks.
The SOE_DATA address range contains the data blocks. The first register of the first data block is
located at the Modbus address Base + 7. Subsequent blocks begin on every 4
th register (i.e. Base +
11, Base + 15, etc.,) as can be seen in the following table:
Offset Description
SOE_DATA + 0 First data block in buffer
SOE_DATA + 4 Second data block in buffer
SOE_DATA + 8 Third data block in buffer
SOE_DATA + 4 * N Additional data blocks (for N = 0 to number of blocks - 1)
Table 25 - SOE_DATA Event Block Locations
7.1.1. Data Blocks
Each data block spans 4 Modbus registers. Data blocks can contain either time-stamp or variable
data. Time-stamp blocks contain date and time information, along with a REASON code. Variable
blocks contain information about specific variable and its value. The BLK_TYPE bit-field in the
HEADER register determines the type of a specific data block.
7.1.2. Time-stamp Blocks
Time-stamp blocks contain a time-stamp for a specific event. Each Time-stamp block spans 4
Modbus registers, and is defined as follows: