Power Measurement 3720 ACM 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 & 16
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 for both devices.
- Baud: 9600
- Parity: None
- Stop: 1
- Mode: RTU Master Mode
- Physical Connection : RS-485 (2 wire connection)
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
|
5
|
0
|
2
|
0
|
0
|
0
|
0
|
0
|
|
N7:10
|
1
|
1
|
5
|
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 N10:251 - 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
|
100
|
3
|
3063
|
2
|
0
|
0
|
|
N7:60
|
1
|
100
|
16
|
200
|
2
|
3063
|
0
|
|
N7:70
|
1
|
100
|
3
|
200
|
18
|
2
|
0
|
|
N7:80
|
1
|
100
|
3
|
5048
|
8
|
20
|
0
|
Our test command list perfoms the following functions.
- N7:50 Read register size and invalid objects settings.
- N7:60 Write 0 to both registers (16 bit data 43064 and Skip Invalid Objects 43065)
- N7:70 Read back status registers (40201,40202,40203,40210,40211...)
- N7:80 Read registers 45049-45056
Cable Connection:
The physical connection which was used during testing was as follows:
|
MCM Module
|
|
Device
|
|
TxRxD+
|
----------------------
|
Terminal RS-485 +
|
|
TxRxD-
|
----------------------
|
Terminal RS-485 -
|
|
RTS
|
------------|
|
Jumper between RTS/CTS on
module must be installed
|
|
CTS
|
------------|
|
|
GND
|
|
|
For ease of installation, termination on the ProSoft module was accomplished using our screw termination adaptor for the DB-25 plug. A similar screw termination plug is also available for the DB-9 required for the 3150-MCM. The part number for these is:
1451-9F : DB-9 to RS-422/RS-485 Screw Terminals (for 3150-MCM)
1452-25M : DB-25 to RS-422/RS-485 Screw Terminals (for 3100-MCM)
Additional Comments and Observations:
- Commands used for testing are designed to prove Modbus communication functionality and not as the basis for any specific application.
- Improper grounding of the unit may cause intermittent communication failures.
- The skip invalid feature will force non contiguous registers to be returned contiguously. As an example, retrieving register 40201 with a length of 10 will return registers 40201,40202,40203 and registers 40210 - 40216
- A request for an invalid register will not return an error.
|
