MPU Dispatch Check Procedure
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4.2. The ModBus Protocol – Message Exchange
Example
This chapter describes the exchange of messages taking place in a
typical Flow Computer - MPU communication.
4.2.1. Modbus Read Message Example
In the following example the flow computer performs the following
task:
- Read temperature and pressure from the MPU Series B
The database objects used for pressure and temperature from an
external source are object numbers 10000 and 10001. These have the
ModBus addresses 20000 and 20002. These registers are read with
ONE message with function code 3. Figure 2 below shows the
contents of this message.
01 03 4E 20 00 04
Node
no.
Function
code
1st register
address
Number of
16-bit values
Figure 2 - ModBus Read Message Example
Note: All bytes are shown in hexadecimal format.
The reply from the MPU Series B will be on the format described in
Figure 3 below.
01 03 08 42 C8 00
Node
no.
Function
code
Pressure - 100 barAByte
count
00 42 16 00
Temp - 37.5 barA
00
Figure 3 - ModBus Read Reply Message Example
The message contains the content of database objects 10000 (pressure)
and 10001 (temperature) represented as two 32-bit real values (least
significant byte first).
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