RS-232 Communication with Polyscience Chiller

[Mike Orgill]

This is my first attempt at RS-232 communication. I am trying to communicate with a Poly-science Chiller using a MicroLogix 1100. I am using the AWT and ARD functions. I toggle each line to true then false but I never get any response from the Chiller nor am I able to change its set point temperature. Please see page 40 of the manual for command formats and the attached for my RSLogix 500 program. Thanks!

 

[Lancie1]

I cannot read your rs232.RSS file. Would you print your RSLogix program to a PDF file? (Set up your Report Options to have only "Program Files" checked, then under the "Program Files" tab, then select only the ladder that contains your Chiller RS232 files.) Post that PDF here, then I might could help find your problem.

 

[Mike Orgill]

I made the configuration changes, but have not been able to export as a PDF. The "Print" button is not active and under "save as" it does not give a PDF option.

 

[Mike Orgill]

I saved it as a Library File (one of the save as options) Does that work?

 

[Mike Orgill]

I Got it to produce a PDF.

 

[Lancie1]

Do you have your RS232 port configured the same as the PolySciene chiller (8,N,1,N, Baud Rate set same)? Do you have the LF (Line Feed) character turned off, with only a CR at the end of each line?

I think that ARL might work better to read a string up to the CR character (instead of reading all the characters that the chiller sends as one long string).

What is in the 12 characters of ST9:0? Does it contain a CR at the end? It appears that most of the chiller ASCII commands are a 2-character command then a CR carriage return, 3 ASCII characters total, except for the 6-character Setpoint command.

 

[Mike Orgill]

Yes, I have configured all RS232 protocol, except for Flow Control (this is not an option). I believe the LF Character is the 2nd termination correct? If so does this matter since I am using AWT rather than AWA?

I have replaced my ARD with the ARL as recommended, but to no effect.

I was messing around using the hex conversion for the RS[CR] command. I changed it back to RS[CR] and now reads 6 characters. I also tried it without the brackets or RSCR.

 

[Lancie1]

Try adding handshaking bits to your AWT and ARD lines. For the AWT use a XIO [CORRECTION] R6:0/EN, inserted after your B3:0/1. For the ARD, use XIO R6:1/EN. These will insure that each instruction is only performed one time for each string. Your original version will try to read and write on each scan of the PLC. For each valid command instruction that you send to the chiller, you will only get one response. Use the Echo command so that you cold read the chiller response with a RS232 Communications intercept program such as Comm Lite.

 

[Lancie1]

I was messing around using the hex conversion for the RS[CR] command. I changed it back to RS[CR] and now reads 6 characters. I also tried it without the brackets or RSCR.

You only need ASCII characters RSCR, no brackets. The brackets indicate the special end-of-line character "Carriage Return".

You should get a 8-character response from the chiller, starting at ST10:0.

Did your configure your RS232 for the ASCII text:

ASCII Configuration
RSLogix 500 - Copyright Rockwell Software
Driver Select ASCII
Baud: Select a communication speed in bits/second.
ASCII = 1200.
Parity Select Even or None to determine whether the parity bit is used in the communication packets
Termination Characters: Termination 1
Specify the first termination character that you use to indicate the end of an ASCII line received. You can specify a single character or a two-character sequence. When specifying a sequence you must also enter a character in the Termination 2 field (below).
Termination 2 Specify the second termination character of a two-character sequence used to indicate the end of an ASCII line received. Retain the default (\ff) if you only specify a single-character termination character.
Protocol Control
Control Line Select No Handshaking for direct point-to-point communication (without a modem).
Select Full Duplex modem.when you require that RTS always be active and transmission take place when CTS is active.
Select Half Duplex modem when you require partial modem control including RTS and CTS modem control lines.
Delete Mode Select the mode of the “delete” character. The delete mode affects the characters echoed back to the remote device. If Delete Mode is enabled the previous character is removed from the receive buffer.
In CRT mode, when a delete character is encountered the controller echo’s three characters to the device, backspace, space, and backspace. This covers the previous character on the terminal.
In Printer mode, when a delete character is encountered the controller echo’s the slash character, then the deleted character.
Echo Enable or disable character echo. When this mode is enabled all of the characters received are echoed back to the remote device. This allows a user connected to a controller with a terminal to see the characters typed.
XON/XOFF Choose software handshaking. XON and XOFF software handshaking involves the XON and XOFF control characters in the ASCII character set. When the receiver receives the XOFF character, the transmitter stops transmitting until the receiver receives the XON character. If the receiver does not receive an XON character after 60 seconds, the transmitter automatically resumes sending characters. Also when the receive buffer is more than 80% full, an XOFF character is sent to the remote device to pause the transmission. Then when the receive buffer drops to less than 80% full, an XON character is sent to the remote device to resume the transmission.
RTS Off Delay (x20 ms)
Select the delay between when a transmission is ended and RTS is dropped. Choose a value between 0-65535 in 20ms increments.
RTS Send Delay (x20 ms)
Select the delay between when RTS is raised and transmission is initiated. When the transmission is initiated the transmitter must verify the CTS signal is active before it can send characters. If the CTS signal is not active the transmitter waits 1 second for the signal to become active. If the signal does not come active within the second the transmission attempt is failed. This feature is only used if full duplex or half duplex modem control is selected. Choose a value between 0-65535 in 20ms increments.
RSLogix 500 - Copyright Rockwell Software

 

[Mike Orgill]

I gave it a try. I did not see a change. Here is a step by step of what is happening: I toggle ACL after doing this my ARD switches to the Error bit (which I believe it is supposed to do) but my AWT stays on the Done bit. I then toggle my AWT this causes the Characters sent to populate with the number 6. I then toggle my ARD the error bit turns off and the enabled bit is turned on. After adding your handshaking bits everything is the same except the ARD error bit stays on and the enabled bit stays off (nothing happens on the ARD).

 

[Lancie1]

After adding your handshaking bits everything is the same except the ARD error bit stays on and the enabled bit stays off (nothing happens on the ARD).

Probably the chiller is not able to read your line, so it doesn't send back a response. I think it is a staight ASCII protocol, so your comm driver has to send only ASCII characters with a [CR] at the end of each line, nothing else. Does your MicroLogix 1100 even allow configuring your RS232 comm port for the old ASCII RSLinx driver? I know the ML1200 and 1500 Series A do not allow ASCII, but the Series B's do have ASCII configuration.

 

[Lancie1]

Do you know that the best way to can tell if you got a response is to look at ST10 in your Data File memory?

You should not see an Error unless:

Execution Errors
The ER (Error) bit is set during the execution of the instruction if:
the instruction is aborted - serial port not in User mode
the modem is disconnected (control line selection is other than NO HANDSHAKING).
the instruction is aborted due to channel mode change.
the UL (Unload) bit is set. The instruction stops executing, but received characters are sent to the destination.
an ACL to clear the receive buffer is executed, removing the ARD instruction from the ASCII queue.
Rockwell Software

 

[Mike Orgill]

Probably the chiller is not able to read your line, so it doesn't send back a response. I think it is a staight ASCII protocol, so your comm driver has to send only ASCII characters with a [CR] at the end of each line, nothing else. Does your MicroLogix 1100 even allow configuring your RS232 comm port for the old ASCII RSLinx driver? I know the ML1200 and 1500 Series A do not allow ASCII, but the Series B's do have ASCII configuration.

How do I configure my RS232 comm port for the old ASCII RSLinx driver?

 

[Mike Orgill]

I am still not getting any response in my ST10. By the way I am using a null modem adapter to switch pins 2 and 3 to match with the chiller.

 

[Lancie1]

How do I configure my RS232 comm port for the old ASCII RSLinx driver?

See the Rockwell Help instructions that I copied in Post #9 of this thread. Your Termination character should be set to CR.