master slave network

[ahuat 0]

happy new year everybody..... :) i made a network of plc with one master and 10 slaves, i use txd rxd function to read datas from the slaves, my problem is if one or two of the slave is swiched off, then the polling is also stop for all the node, how to make the program continuing do a polling to another node. if anybody can give a share pls help... thank you in advance ahuat

[BobB 58]

How did you do it? Modbus? Serial? I normally use Controller Link. No problems then.

[ahuat 0]

i use serial, because the slave plcs are cqm1h-cpu21,

[BobB 58]

Firstly I would suggest you use RS232/485 converters for multi drop. The Adam units are very good. I normally use the Adam 4520. www.advantech.com Secondly this link may help you, I do not really know. I do not even use CQM1 any more now that CJ1M is so cheap. RXD/TXD samples This may also help Modbus missing nodes Edited 3 Jan 2005 by BobB

[ahuat 0]

thanks for your reply BobB :) i do use rs232 to rs422 converter, the link in txd rxd is what i do for the programming, the problem is, if one of the node is swiched off, then the master always stop the txd rxd after reached the swiched off node. the second link is interesting, but i don't know how to do it in txd rxd function, do you have an example ? regards ahuat

[Nibroc 4]

You may need to post your ladder program to allow us to take a look. It is possible that your sequence is not 'advancing' to the next PLC when no reply is received from the switched off PLC. I usually use a timer to detect if a reply is received after the txd is executed - ie check that reception complete flag turns on (AR8.06) within a short time after txd Should no reply be detected, reset the port (port reset bit) to ensure the receive buffer has no 'garbage' in it before executing the next txd. Regards Nib

[ahuat 0]

thanks for the reply Nibroc the attachment is the ladder, pls inform what do you mean by reset the port bit ... thank you in advance. regards ahuat node1to5.cxp

[ahuat 0]

more information about the ladder node 1to5 channel 1000 is the node number, A392.05 is ready to transmit bit A392.06 is receive complete bit timer 0 to 5 is a delay for each transmission best regards ahuat

[Sleepy Wombat 27]

Firstly, if you enable the node again does the program happyily work again ?... If so with out looking at your program (time is very short at the moment) can you use the recieve flags with a timout to go to the next node ? Sorry about not provinding more info ...

[ahuat 0]

no, i have to restart the master plc... ahuat

[Nibroc 4]

The RS232 port restart bit is A526.00 for a CJ1 series PLC. I have added this to your program as attached. Looking at your code it seems that the master PLC will stop polling if no valid reply is received. This will occur if: - a slave PLC is switched off - the reply is incorrect or corrupt and does not terminate with the correct end code (0x000D) I have attached a suggested fix to try, this will skip to the next node if no reply is received. This ladder code will also not write any data to the PLC memory if a node does not reply (ie the last valid reply from the node will remain). TrialFix.cxp Edited 4 Jan 2005 by Nibroc

[ahuat 0]

Hello Nibroc... ... thanks a lot......, i give us more information on what's happen in txd rxd operation.... again, best regards from all of us ahuat

[Sleepy Wombat 27]

Thanks Nibroc for your efforts...