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.