Watlow Series 988 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 & 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 performed with the following settings used:
- Baud: 9600
- Parity: None
- Stop: 1
- Mode: RTU Master Mode
- Physical Connection : RS-485
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
|
0
|
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 N10:199 - 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
|
7
Polling
Time Preset
|
|
N7:50
|
1
|
1
|
3
|
0
|
10
|
0
|
0
|
0
|
|
N7:60
|
1
|
1
|
4
|
10
|
10
|
10
|
0
|
0
|
|
N7:70
|
5
|
1
|
6
|
200
|
1
|
7
|
0
|
0
|
Our test command list performs the following functions.
- N7:50 Read registers 40001-40010
- N7:60 Read registers 30010-30020 (same registers as 40010-40020)
- N7:70 Write to register 40008 (function 16 could also be used in this position)
Cable Connection:
The physical connection which was used during testing was as follows:
|
3100-MCM
Module
|
|
Series 988
|
|
14 TxRxD+
|
--------------------
|
Terminals 5 & 3
|
|
25 TxRxD-
|
--------------------
|
Terminals 6 & 4
|
|
4 RTS
|
-----------|
|
|
|
5 CTS
|
-----------|
|
|
Additional Comments and Observations:
- RS-485, was used for testing purposes.
- The maximum length for any read is 32 words in length.
- Watlow recommends avoiding continuous writes to the unit. This can be easily avoided by using the conditional of port command. This will cause the command to execute based on a change of values in the source data. A second option would be to use the command control functionality available in version 2 of the 3100/3150-MCM. For further information on how this may be done please contact us to obtain a copy the sample logic illustrating this functionality.
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