IMPACC Modbus Gateway connectivity to 3100-MCM
Problem Solution Overview
We performed testing between the subject device and our 3100-MCM product.
Solution Brief
Our testing generated the following results:
- We were able to successfully communicate with the device. (see below for configuration parameters used during the testing)
- The product supported Modbus functions 3, 4 & 6 (see notes)
- Message turn around for this unit averaged 10ms at 75% gateway speed.
The purpose of our testing is to assure a level of compatibility in the communications between the two products. Through this testing, we attempt to identify problem areas that may arise when implementing the interface in the field.
Configuration:
The product testing was perfomed with the following settings used:
- Baud: 19200
- Parity: None
- Stop: 1
- Mode: RTU Master Mode
- Physical Connection : RS-232
The Module Configuration used in our testing was as follows:
|
Address
|
0
|
1
|
2
|
3
|
4
|
5
|
6
|
7
|
8
|
9
|
|
N7:0
|
0
|
0
|
6
|
20
|
0
|
0
|
0
|
0
|
0
|
0
|
|
N7:10
|
1
|
1
|
6
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
|
N7:20
|
4
|
1
|
2
|
130
|
150
|
0
|
0
|
0
|
4
|
0
|
This configuration, in combination with the example ladder logic referenced below, generates the following memory map:
N10:0 to N10:129 - Slave Data
N10:130 to N10:149 - Slave Error Table (Contains revision level information also)
N10:150 to N10:199 - Master Error Table (Contains status of commands for diagnostics)
Command List:
The following command list shows some of the commands which were used to test the communications:
|
Address
|
0
Port
Number
|
1
Slave
Number
|
2
Function
Code
|
3
Source
Address
|
4
Count
|
5
Dest
Address
|
6
Read
Type
|
|
N7:50
|
1
|
1
|
3
|
0
|
10
|
0
|
0
|
|
N7:60
|
1
|
1
|
4
|
0
|
10
|
20
|
0
|
|
N7:70
|
1
|
1
|
6
|
200
|
1
|
0
|
0
|
|
N7:80
|
1
|
1
|
16
|
201
|
10
|
0
|
0
|
Our test command list perfoms the following functions.
- N7:50 Read 10 words of the holding registers.
- N7:60 Read 10 words of the input registers.
- N7:70 Write 1 word to the holding registers.
- N7:80 Write 10 words to the holding registers. (undocumented support, see notes)
Cable Connection:
The physical connection which was used during testing was as follows:
|
3100-MCM
Module
|
|
Modgate Comm
Port
|
|
2 TXD
|
-----------------
|
RXD
|
|
3 RXD
|
-----------------
|
TXD
|
|
7 GND
|
-----------------
|
GND
|
|
4 RTS & 5 CTS
Jumpered
|
|
RTS/CTS
Jumpered
|
Additional Comments and Observations:
- Although the documentation makes no mention that we could find, the unit also appears to support function 16.
- This unit honors the implied address ranges used in the Modbus protocol, consequently you will need to use the appropriate function to access the 30000 and 40000 registers.
- We recommend setting the Gateway Duty Cycle to no greater then 75%.
- Error codes for register writes may be retrieved by reading back the register in question.
- Register assignments are user determined by the mapping of the IMPACC network devices in the Modgate application.
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