hardware-simple-converter
Hardware:Simple converter
Introduction
The converter offers the most economic solution in order to connect a PC to Profibus DP network. Another requirement is the connected PC should have a serial port. Electric level RS-232, generated by common PC, is converted using this dongle to RS-485, used by Profibus DP. The dongle is powered directly from the serial port of the PC. It is a reason why the converter is very small with very few components integrated. The disadvantages of the solution is that it's not possible to use the dongle in very extensive network with long cabling, further it's not possible to use cable termination and the number of nodes on the network is limited to around 10 nodes.
The highest Profibus speed of this converter is only 19200 baud. The limitation is incurred by the disagreement of speeds supported by the standard serial port of the personal computers and the speeds supported by Profibus DP. The following table illustrates the situation:
| PC's Serial Port | 9600 | 19200 | 38400 | - | 57600 | - | 115200 | - |
|---|---|---|---|---|---|---|---|---|
| Profibus DP | 9600 | 19200 | - | 45450 | - | 93750 | - | 187500 |
Schematic
Converter RS-232/RS-485 schematic
Null Converter
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You may like to test the drivers but don't have any hardware? You can do just few simple loopback wiring as the following
TxD(3) - DSR(6)
RxD(2) - CTS(8)
TxD(3) - RxD(2) -
I have tried by soldering only the D-SUB connector on a converter board as on the picture above (without any other components, just a 5kOhm blocking resistor between TxD and RxD - may be not necessary)
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Define a macro PBM_NULL_CONVERTER in pbm_8250.h and recompile the modules. You may want to increase the PBM_DEBUG_LEVEL in pbmcore.h so you will be able to see how the drivers is "running". Follow this link for the installation of the modules.
