| ??? 12/26/12 21:12 Read: times |
#189035 - Could the data rate be a problem? Responding to: ???'s previous message |
Mahmood Elnasser said:
I used the MAX483 chip with its Vcc connected to regulated 5V supply for my 7 clocks with a network of around 100 meters. It worked for a couple of years now. Customer expanded his firm and ordered another 7 clocks to be added to the network, 1 on the 5th floor one on the second floor and 5 on the 1st floor where the old 7 clocks are located. Looks like the trip to the 5th floor and back to 2nd floor and back to 1st floor took another 100 meters of length.
I noticed 2 of the 5 clocks at the end of line do not receive the data, I measured the amplitude of the RS422 signal and it was very low less than 0.5v. So I made RS422 repeater board for the last 5 clocks and supplied them with 5Vdc Vcc which solved the problem. Thinking about the problem again (After it has been solved) I noticed that MAX48x chips are rated for 12Vdc supply. If I raised the Vcc of my master MAX483 chip to 12Vdc, probably I don't need the repeater board to extend the range and would have saved my self one day of work. What Vcc supply voltage do you use for your RS485/422 applications? Mahmood ...RS-485
Standard EIA RS-485
Physical media Twisted pair
Network topology Point-to-point, Multi-dropped, Multi-point
Maximum devices 32 - 256 devices (32 unit loads[1])
Maximum distance 1200 metres (4000 feet)
Mode of operation Differential signaling
Maximum baud rate 100 kbit/s - 10 Mbit/s
Voltage levels -7 V to +12 V
Mark (1) Positive Voltages (B-A > +200 mV)
Space (0) Negative voltages (B-A < -200 mV)
Available signals Tx+/Rx+, Tx-/Rx- (Half Duplex)
Tx+, Tx-, Rx+, Rx- (Full Duplex)
Connector types Not specified
The supply voltage for your drivers/receivers/transceivers would depend entirely on the manufacturer's spec's. Clearly, if the intended voltage levels exceed 5 volts, the supplies will also have to do that. It's differential signaling, however, and if you measure both Rx+ and Rx-, in differential mode with your 'scope, and still get only 1/2 volt or so, check your receiver spec's, as some will tolerate that low a differential voltage. You are getting the "eye" level, are you not? I've always had bipolar 5 volts available, though I don't recall every going below GND on my app's, which were always short-haul, unlike yours. This signaling protocol should easily allow 10 Mbits per second. I'd look for a fault in the cabling or perhaps a faulty connector before making any circuit alterations. RE |
| Topic | Author | Date |
| RS485 supply voltage | 01/01/70 00:00 | |
| Could the data rate be a problem? | 01/01/70 00:00 | |
| 5V | 01/01/70 00:00 | |
| No! | 01/01/70 00:00 | |
| Strange! | 01/01/70 00:00 | |
| stubs? | 01/01/70 00:00 | |
| Found it | 01/01/70 00:00 | |
| I made $$ on that one | 01/01/70 00:00 | |
| How to Protect ? | 01/01/70 00:00 | |
| Use MAX3430 | 01/01/70 00:00 | |
| Or the LT1785... | 01/01/70 00:00 | |
| MAX485 | 01/01/70 00:00 | |
low | 01/01/70 00:00 |