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 .