Hi there,

I am using an AB ML 1200 series C PLC to control a weigh feeder.Also connected to ML's Channel 0 is a Network enabler card by Moxa(never worked with this before).I have to send out several process parameters to this Network enabler by first converting the integer values to strings and then writing each one to the Channel 0.If I am right then the ASCII write instruction would take about 0.5 sec to execute.And to write about 10 different strings would take approximately 5 sec.(pretty long)

The channel 0 is configured to ASCII protocol.And I am simply writing string after string to the channel,with a delay of 0.5 sec for each string.

Can some one suggest a better way to do this??Can someone let me have a sample code for Serial communication??I havent yet tested my code,but the time taken for this communication routine would really increase the scan time of the entire program.

Thanks in advance for you suggestions and help.

Sajid,

Your ASCII instructions are going to be processed in the background during your ladder diagram program. The execution of the ladder diagram does not wait for the ASCII instruction to finish transmitting all characters, but rather moves the data to a buffer and the transmission is handled by the MicroLogix operating system.

How are you calculating 0.500 seconds for an ASCII string transmission ? At 9600 baud with standard "8/N/1" ten-bit serial framing, an 82-character MicroLogix string (the maximum size in this controller) only takes 820/9600 = about 85 milliseconds.

What is the MOXA device going to do with the ASCII data once it arrives ?

Sajid,
Just a thought because I do not know where the ascii goes once it reaches the Moxa Serial to ethernet unit, but the Micrologix 1100 comes with a built in ethernet port and might allow you to eliminate the MoxA converter. Worth discussing with your Local Rockwell rep if you are still in the design stage and can change processors.

Hi,

Well thanks for your help and suggestions.Well I just tested my set-up and I should say that it worked really nice.The MOXA card accepts serial data and converts them to TCP/IP packets to be transmitted over a network using TCP/IP protocol.It is rather a network enabler.Since my customer had specifically asked for ML 1200 series C,I did not have any chance to go for any other processor.So I guess I will have to work with whatever I've got.An ethernet module on the expansion bus would have added to the cost of this project and I should say that with a little bit of good programming with the PLC the MOXA card can really help in achieving the task,and its costs very less.

I was a bit curious about how the other instructions in the ladder would be executed when this communication is happening at the same time.I will check on that.

And once again thanks a lot for for help.I'll go refine the ladder.

Sajid.