bjump

Hi, I need to implement ladder logic that calculates a 16-bit CRC value for modbus commands. I know the algorithm, but I am struggling putting it into ladder. Any help would be appreciated.

Can someone please show me an example using RCV and XMT without using interrupts? I have not been able to get this to work properly. I can get it working with interrupts, but I do not want to use the interrupts for my application.

b_carlton, Thanks a bunch! I never though of using the Done bit to reset the timer. This is very helpful.

Thanks for the help! I have just one question. If the "standby" conditions are true for this entire time, how does the 1 minute timer reset when its constantly being triggered by these conditions? Also, the timer would not be retentive. It just needs to reset every time the "standby" conditions are false.

I'm using RSLogix 500 and I need to time how long a set of conditions has occurred. Basically, I know that if this set of conditions are true, then the machine is standing by. If the machine has been in standby mode for 72 hours, I want to start it up and run it. How could I do this without having to use 9+ timers? I need to stop the timing if the conditions become false. But as long as they are true, I want to time up to 72 hours.

Hey all, I am trying to interface an old modem/radio with the S7-200. Trouble is, the modem uses the RTS signal to key the transmitter. Well the S7-200 RTS signal does not hold constant during the entire data transmission. I believe that it just pulses before the data from the S7-200 is transmitted. I've also tried to use SM4.5 to trigger one of the dry contacts which is hooked to the radio's transmitter. The problem is, the SM4.5 goes low as soon as data starts transmitting. By the time the contact closes and the radio transmitter keys, most of the data has already been sent out by the PLC. Can anyone think of anyway I can key the transmitter some time before the port's transmission begins? I am communicating modbus and using the MBUS_INIT and MBUS_SLAVE function blocks.

The customer is replacing over 90 of the old Modicon Micro's with S7-200's. Therefore, buying over 90 new modems is not an acceptable solution.

Hello all, I have an S7-200 that I am trying to connect to a modem via a PPI cable. The radio attached to the modem will key its transmitter upon receiving the RTS signal from the PLC. The problem I am having is, as soon as I switch the PPI cable to DTE, which allows it to utilize the RTS signal, the radio is in continuous transmission. This leads me to believe that the PLC/PPI cable is constantly sending a RTS signal to the modem. Would there be any cause for the PLC to do so? Is this a flow control issue? Please help.

Hey all, I am trying to figure out if I can communicate Modbus and remotely program an S7-200 and keep the same dip switch settings on the PPI cable. Basically, the S7-200 sits behind a modem, which receives modbus commands from a Modicon Momentum via the radio. What I would like to be able to do, is remotely change the port mode on the S7-200 from Modbus to PPI and then program the S7-200 and then switch the port back to Modbus mode. I have figured out ways I am able to switch the port back and forth, but I think the only thing that prevents me from doing this is the dip switch settings on the PPI cable that runs from the modem to the S7. I think they would have to be changed in order to switch from receiving modbus to PPI commands and vice versa. I will continue to research this, but if anyone has any suggestions, I would greatly appreciate it.

Ian, Thank you. I will try this.

Hello, I was wondering if there is an easy way to monitor the addresses VB1000 to VB1180 in the Step 7 programming software? I am using the status chart now, but I am unable to find an easy way to input all those addresses.

Hey all! Has anyone ever hooked up a Modicon Momentum to an S7-200 and had the two talk modbus? More specifically, with the Momentum as the master and the S7-200 as the slave.

Hey all! Has anyone ever hooked up a Modicon Momentum to an S7-200 and had the two talk modbus? More specifically, with the Momentum as the master and the S7-200 as the slave.

Hey all, I am using the XMIT function block to send modbus commands to RTU's. I would like to somehow monitor the sending of those commands. Is there a way to do so? Is there a way to hook the RS485 into my serial port and see what is being sent?

I have posted the modbus request above Basically, I have a wonderware application which collects data from a data concentrator. The data concentrator, the Modicon Momentum, sends polls the multiple RTU's via radio to collect data from each. The above posted request is sent out by the data collector to the RTU's. Currently, the RTU's are Modicon Micro's. They seem to handle the request just fine. The Siemens S7-200 does not recognize the request. I am not sure what type of Momentum is there, I am making a return trip tomorrow (The system is 2 hours from our office). I am going to record the modbus request post modem at the data concentrator and and post modem at the remote test station.