| ??? 12/02/09 07:35 Read: times |
#171378 - Not very helpful Responding to: ???'s previous message |
Kamran Rasul said:
I have a another PLC with standard Modbus running and it captures the requires value from the desired PLC and displays it on its own screen. So, it is sure that the desired PLC is working. So you need to examine the communcations between those two PLCs and see how they differ from what you're doing with Hyperterminal and your MCU - don't you? The Modbus program don't receive any answer, no error message or anything. See above. How do you know that 9600 baud is the correct speed?
-The desired PLC is communication with another PLC at modbus (RS232) But how do you know that it is communicating at 9600 baud? How do you know that there shouldn't be any parity?
-Should there be any...? It is you job to find that out! What do the PLC's Manuals say? How do you know that your null-modem cabling is correct?
-The same is working with another PLC... But how do you know it's right for use with a PC? How do you know that your null-modem cabling is correctly connected?
-The same is working with another PLC... See above. How do you know that the device is using RTU?
-The other PLC is working in both modes with the desired PLC... So look at the comms - and spot the difference! How do you know that the device have Modbus enabled?
-The same is working with another PLC... Maybe they do some "negotiation" to get it started...? Maybe there are additional control signals - that you're not (correctly) implementing with Hyperterminal? How do you know that the request is reaching the device?
-If the Hyper Terminal is receiving the message then the PLC should No, that doesn't follow at all! How do you know that the device isn't answering, but the answer not reaching the PC?
-This is not possible,I am handling the Rx, Tx with separate MCUs Pardon? How do you know that your timing is ok?
-In the same scenario of the other PLC... See above. |
| Topic | Author | Date |
| Modbus | 01/01/70 00:00 | |
| What testing have you done? | 01/01/70 00:00 | |
| Don't use hyperterminal | 01/01/70 00:00 | |
| modbus | 01/01/70 00:00 | |
| modbus | 01/01/70 00:00 | |
| Still lots of debugging left | 01/01/70 00:00 | |
| Modbus | 01/01/70 00:00 | |
| Not very helpful | 01/01/70 00:00 | |
| Modbus | 01/01/70 00:00 | |
| Still need to break the problem down into smaller steps | 01/01/70 00:00 | |
| Modbus | 01/01/70 00:00 | |
| modbus | 01/01/70 00:00 | |
| modbus | 01/01/70 00:00 | |
| Parity | 01/01/70 00:00 | |
| Oscilloscope results? | 01/01/70 00:00 | |
| open source | 01/01/70 00:00 | |
| Also RTU Framing | 01/01/70 00:00 | |
| Framing, addressing etc has been discussed | 01/01/70 00:00 | |
| modbus | 01/01/70 00:00 | |
| Bad CRC order!! | 01/01/70 00:00 | |
| modbus | 01/01/70 00:00 | |
| modbus | 01/01/70 00:00 | |
| Don't know why, | 01/01/70 00:00 | |
| Comparison with something known working | 01/01/70 00:00 | |
| what device address | 01/01/70 00:00 | |
| modbus | 01/01/70 00:00 | |
I would do this... | 01/01/70 00:00 |