Transmission Area Format in a PLC

The format for a compound message in a transmission area is:

Description Size (in bytes)
Format 2
Reserved 2
Number of Sub-Packets 2
Sub-Packet 1 Domain 2
Sub-Packet 1 Domain Offset 2
Sub-Packet 1 Length 2
Sub-Packet 1 Timestamp 8
Sub-Packet 1 - first data word
.
.
Sub-Packet 1 - last data word
.
.
Sub-Packet n Domain 2
Sub-Packet n Domain Offset 2
Sub-Packet n Length 2
Sub-Packet n Timestamp 8
Sub-Packet n - first data word
.
.
Sub-Packet n - last data word

Where:

  • Format must be 1.
  • Number of Sub-Packets is the number of Simple Messages contained in the Compound Message.

Each sub-packet is essentially a Simple Message that has a common header and a variable length data area. The sub-packet header is as follows:

  • Sub-Packet Domain - the PLC data type from which the data in the Sub-Packet originates. The contents of this field will be a number representing the data type as follows:
Value PLC Data Type
0 Local Data Block (%L) 90/70 Only
8 Register table (%R)
10 Analog Input table (%AI)
12 Analog Output table (%AQ)
16 Discrete Input table (%I)
18 Discrete Output table (%Q)
20 Discrete Temporary (%T)
22 Discrete Internal (%M)
56 Genius Seamless (%G)
24 Special Contacts A (%SA)
26 Special Contacts B (%SB)
28 Special Contacts C (%SC)
30 System Fault , (%S) read only
  • Sub-Packet Domain Offset - the domain start address of the data in the Sub-Packet. This field is numeric and quoted in units of the domain data type starting at zero.
  • Sub-Packet Length - the length of data in the Sub-Packet. This field is numeric and quoted in bytes.

If the Sub-Packet domain is %L, then the first 8 bytes of data contain the block name for the %L domain.

  • Timestamp -the time relating to the data in the Sub-Packet, in CIMPLICITY COR_STAMP format .