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Om kommunikationen inte fungerar så följer här en beskrivning hur du själv kan testa gränsnittsomvandlarens funktion. Skulle omvandlaren, efter testerna, ändå inte fungera, tag kontakt med oss eller närmaste distributör så hjälper vi dig.
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- This is simple to check, the PWR LED on the front panel will be on. If it is not check that the power cable is properly inserted and that power is available. There is an internal fuse (however it is unusual for this to blow), but it is worth checking if there have been power supply problems.
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- To perform this test you should set the internal DIP-switches back to the factory default settings. That is transmitter always active, CTS always high, DCD always high, 4-wire and no termination.
n.b. before opening the unit please ensure the power is switched off
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- The converter is configured as a DCE (Data Communication Equipment), the serial ports on a PC are DTE (Data Terminal Equipment). This means that a standard modem cable is all that is needed.
| 9-pole PC connection |
25-pole PC connection |
|
MA-45 |
PC |
|
MA-45 |
PC |
| TD |
2 |
3 |
TD |
2 |
2 |
| RD |
3 |
2 |
RD |
3 |
3 |
| RTS |
4 |
7 |
RTS |
4 |
4 |
| CTS |
5 |
8 |
CTS |
5 |
5 |
| DSR |
6 |
6 |
DSR |
6 |
6 |
| SG |
7 |
5 |
SG |
7 |
7 |
| DCD |
8 |
1 |
DCD |
8 |
8 |
| DTR |
20 |
4 |
DTR |
20 |
20 |
| 9-pole PC connection |
25-pole PC connection |
|
MD-45 |
S-T |
PC |
|
MD-45 |
S-T |
PC |
| TD |
3 |
8 |
3 |
TD |
3 |
8 |
2 |
| RD |
2 |
7 |
2 |
RD |
2 |
7 |
3 |
| RTS |
7 |
6 |
7 |
RTS |
7 |
6 |
4 |
| CTS |
8 |
5 |
8 |
CTS |
8 |
5 |
5 |
| DSR |
6 |
2 |
6 |
DSR |
6 |
2 |
6 |
| SG |
5 |
1 |
5 |
SG |
5 |
1 |
7 |
| DCD |
1 |
4 |
1 |
DCD |
1 |
4 |
8 |
| DTR |
4 |
3 |
4 |
DTR |
4 |
3 |
20 |
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- To do this take the 5 pos. screw terminal connector and connect pin 1 to pin 3 and then connect pin 2 to 4. Any short piece of cable is suitable.
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- With all the connections made the converter will have the PWR, DCD, CTS, RTS LEDs on and the RD and TD LEDs off. The next step is to run up a terminal software program such as Windows terminal on your PC. When you type characters on the PC keyboard they should echo on the screen and simultaneously you will see RD and TD flicker to indicate data flow.
If all this works then there is nothing wrong with the converter.
- If this test fails then quickly check the system. If the RD and TD LEDs donít flicker then no data is leaving the PC, check which port the PC is configured for and then make sure the cable is firmly connected. If only the RD light flashes and no data throughput is noted check the screw terminal connector.
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- There can be many reasons why RS422/485 communications wonít work so here are a few possibilities.
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- If you are using the converter in a 2-wire system or as a slave in a 4-wire multidrop configuration then your PC will have to provide a signal to control tristate on the driver chip. The most common solution is to use the RTS line for this control. In the converter you will need to set up DIP-switches on S2 to allow this RTS control.
- There will be occasions when RTS is not available. In this case the contact Westermo about the MA/MD-45 which can perform line switches on data flow alone.
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- It is all to easy to get your positives and negatives muddled up. If you should notice that the RD LED is on full then you can be sure that either you have the lines incorrectly wired or when the lines are inactive they have floated (see fail-safe and termination) to an incorrect state. It is often worth just exchanging connections at this stage. From experience we have discovered that labelling on some interfaces can be misleading so using the converters LEDs can save a lot of time. Remember when no data is on the line TD and RD will be off, when there is data you will see these two LEDs flicker.
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- If you read into RS-422 and RS-485 you will discover that line termination’s are to be recommended. On 4-wire systems just the last receiver should have a 100 ohm resistor as a terminator and on 2-wire RS-485 systems both ends of the line should have similar terminators. The converter has an option to allow these termination’s to be set up by dipswitch, however we also have a fail-safe circuit that comes into effect with the termination.
- Fail-safe is a simple biasing circuit that ensures that the line is always in a known idle state when there are no active transmitters on the line. With 2-wire systems this happens most of the time. If you have already tried inverting the line polarity change the connections back the way they were and try switching in the fail-safe circuit on the converter.
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- Pin 5 on the Screw terminal is not connected to earth, but to an isolated 0V. Pin 5 can be used in various ways. By connecting it to the equipment 0V connection a reference is provided for the communications. Do not use the cable shield for this. If you have a shielded cable then it is best to separately ground the shield to a good earth at a single point as close to the end of the line as possible. If you have no earth points then you can connect the shield to pin 5, but do not make any other connection or you could induce earth currents.
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