| ??? 12/02/09 08:20 Read: times Msg Score: +1 +1 Good Answer/Helpful |
#171380 - Still need to break the problem down into smaller steps Responding to: ???'s previous message |
No need for bold text. Your Modbus test programs probably already knows how to talk Modbus.
1) Connect PLC to PLC. 2) Look at the serial data between them. What baudrate? Parity? 3) Connect PC to PLC. 4) Does the serial data reaching the PLC look the same? 5) Create a sniffer cable where the RX signal from PLC1 to PLC2 is sent to one serial port on PC, and the TX signal to another serial port on the PC. 6) What data does the PC pick up from PLC1? What data does it pick up from PLC2? What is the difference compared to the info your PC tries to send? Your task is to figure out the difference between the combinations that works, and the combinations that doesn't work. Either reading all documentation and figuring out what may be wrong. Or by using a bit of test equipment and measuring what is happening, and comparing to what you expect should happen. |
| 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 |