Figure 5-7. Modbus Plus Message Frame Structure; Figure 5-8. Modbus Plus Token Rotation Explanation; Figure 5-9. Modbus Plus Token Rotation Explanation - ABB TPU2000 Technical Manual

TPU2000/2000R Modbus/Modbus Plus/ Modbus TCP/IP Automation Guide
MAC
Modbus Plus is a "token passing" network in that upon startup, a token is generated. The node with the token
acts as a host device. The node holds a token for a period of time and passes the token to the next node on the
network. The token rotation scheme is described in Figures 5-8 through 5-10.
OPENING FLAG OPENING FLAG
PREAMBLE PREAMBLE
7E 7E
AA AA
(SYNCH FLAG) (SYNCH FLAG)
DEST SOURCE
ADDRESS ADDRESS
MASTER
ROUTER
OUTPUT
COUNTER
PATH

Figure 5-7. Modbus Plus Message Frame Structure

PEER TO PEER EXAMPLE
2 4
1 3
55 57 58
56
List: 1,2,3,4,5,
55,57,58,64
1 2 3 4
55 57 58
56
List: 1,2,3,4,5,
55,56,58,64

Figure 5-8. Modbus Plus Token Rotation Explanation

2 4
1 3
55 56 57 58
List: 1,2,3,4,5,
55,56,57,64
2 4
1 3
55 56 57 58

Figure 5-9. Modbus Plus Token Rotation Explanation

BROADCAST BROADCAST MESSAGE MESSAGE
ADDR ADDR
FF FF
FUNCTION
COMMAND INCLUSION
CODE
( INCLUDES MODBUS)
TRANS
ROUTING
SEQUENCE
PATH
NUMBER
Each node on the Network has a list
5
of all other node addresses on the
network. Upon Startup a token is
generated. The node in possession of
the token (Red Spot) may transmit.
64
When the node has finished
transmitting, it passes the token to
5
the next node. This node may, for
instance, may not wish to transmit.
The token will be passed to the next
64 node in the list before its time has
expired.
5
If so the token is passed to the next
node, which sends a message...
64
5
... and so on in a fixed sequence
so that every node is guaranteed
network access within a
predetermined time slice.
64
List: 1,2,3,4,5,
55,56,57,58
CLOSING CLOSING
CRC-16 CRC-16
FRAME FRAME FLAG FLAG
CHECK CHECK
MODBUS
FRAME
42