I presume the 2-port variant MCS7820 would also work seamlessly. They work straight off on current Raspbian 'stretch'. They are commonly available on eBay for about US$20-$30.
Also - FYI - I have had no issue with the MCS7840 adaptors (USB to 4-port RS232). So I am not saying every HL-340 based adaptor eve3ry produced will fail. The RS232 voltages are generated by a transceiver chip after the HL-340. I have had no problem with the PL2303 USB to Rs232 adaptors. The HL-340s gave about 0 to +3v.īut voltages are good from the PL2303 adaptors I have used.
I then checked the RS232 data pins on an oscilloscope. I plugged in an alternative adaptor (using the PL2303 chip) and there was no problem. I know this because I bought some and could not get them to work. More specifically, they do not generate the correct voltage swings on the RS232 TxD pin. The HL-340 USB-to-RS232 adaptors I have seen (& purchased on eBay) seem to be all *defective*. Cursor position changed for some keys is it converter problem? Or is there any method to connect PLC with raspberry pi via modbus protocol? This is a very late posting and perhaps this is not any issue anymore. 1 download zip file of above adapter driver for Linux 2 extract it 3 run make command 4 connect USB serial adapter to raspberry pi ( I connected pin 2 and pin 3 of serial port together) 5 run putty on raspberry and select serial and type port as ttyUSB0 and clicked open 6 then new windows was popup and when i type on keyboard there is no any letters appear. I need to use a USB to Serial adaptor but can't get the driver to load.
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