RS232
Dear gentlemen,
the EIB RS232 devices ALL pull current out of the PC's RS232 lines.
Ground: EIB is SELV. PC's are not. A galvanic separation between both is mandatory (safety aspect).
Thus: the part of the RS232-device "on the PC side" needs to be powered.
* This could be done in an expensive way, transferring power of the galvanic separation (using a transformer). Not done.
* This could also be done by using an extra power supply (net adapter). Not done.
* The cheaper solution was opted for: take the current from the RS232 port.
Now:
- some RS232 devices draw current from the signal lines (RTS, CTS, TxD, RxD) only.
- other devices (most) additionally use DTR.
- some use ALL RS232 lines, and even have voltage pumps and invertors.
Now:
some RS232 devices are happy with 'less' power, using opto-couplers and electronics requiring less energy.
Meanwhile,
PC manufacturers provide PC's with SubD-9 connectors, claiming compliance to the RS232 standard, where at best they only comply to the RS562 standard. Mostly worse.
PC's that have fully RS232 compatible ports have no problems.
Mr. Steven De Bruyne
System Department - KNX Association
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