Monarch76 (Customer) asked a question.
Looking for guidance on ASCII "Send" message from Click Plus to a temperature controller via RS485.
Wondering if there is anything wrong with the send message I created by reviewing the few screenshots I provided. From everything I can tell the comms parameters are properly matched and I think I am using the correct syntax. I have 120ohm resistors at both ends of the cable and I'm using twisted/shielded cable with drain wire landed at one end (also tried with both ends). The cable is only 25 feet long.
The send instruction is intended to change setpoint on the temperature controller to 37 Celsius. I appreciate the help, in advance.
I have only worked with the RS232 port which worked OK.
Maybe the SC43 error flag provides some clue. Looking at some other info seems like the message must begin with a full colon and end with CRLF.
From AI: Framing: Starts with : (0x3A), ends with CRLF (0x0D, 0x0A).
A typical ASCII message looks like: :<Address><Function><Data><LRC><CRLF>
Are 2 stop bits really needed?
Why not use the Modbus RTU protocol? seems to be more efficient.
https://www.prosoft-technology.com/kb/article.php?id=382
The receiving/slave unit only allows for RS485 comms. I set the PLC comms based on the default values provided by the chiller/heater unit which were as follows:
Is this temperature controller one of ours? If so what is the model?
I should have been more descriptive. It is a circulating chiller/heater from SMC. Model number INR-244-831.
Are you trying to send the following command to your SMC device?
<STX><Address><Read/Write><Identification><NumericData><ETX><BCC>
STX: Embedded ASCII Code ($02)
Address: "01"
Read/Write: "W"
Identification: "SV1"
Numeric Data: "00370"
ETX: Embedded ASCII Code ($03)
BCC: "Q" (or 0x51)
One of the messages I was trying to send looked like this:
I created the message based on the following example provided by the manufacturer of the chiller/heater:
In your send instruction you have created a string of ASCII characters. On the wire, these will be transmitted as their hexadecimal equivalents, which is not going to provide the SMC device with the string of characters it is expecting. For example, the first two characters in your string are "02". This will translate to 0x30 0x32 in the transmission. It will NOT translate to 0x02. For the STX and ETX, you'll need to use the embedded ASCII characters 0x02 and 0x03.
Below are some images of the string of characters I think you are hoping to send to the SMC device. Take a look at the SEND instruction from the CLICK programming software.
Thanks very much! I will give this a try and report back.
The Click Plus software is telling me I need " at the beginning of the string
Maybe try encoding all the bytes as embedded ascii enclosed with double quotes: