Resurrecting a 605x for programming may be an intellectual exercise, however I would caution against frustration - given modern two-way , peer<>peer options.

Unless you know you have a good 6050, be prepared for the possibility that a 2nd hand one may be faulty.
However, I am not sure that flagging this forum thread as a Bug is appropriate.

You appear to have the COM setup definition correct 2400,8,N,2
However you may also want to confirm your wiring (loopback 1-4-6 for 9 pin D Serial port) at the PC side.

For 1st level connectivity testing I would suggest getting the Stop/Go to work before delving into Locomotive commands
Stop = one byte = x64(96 dec)
Go = one byte = x65(97 dec)

The loco commands are 2 byte
Byte 1 = speed 0-14 (15 = reverse)
ANDed with x10(16 dec) from the main function
Byte 2 = loco address (1-80)

for any string of command your programming MUST manage the delay between commands as there is no buffering in the 6050 and it must finish processing the first command before it will accept a second - any commands sent before it is ready will be lost.
The delay will vary depending on the command type. This is particularly important for turning the pulse to a turnout off.

Thank you so much for your quick answer to both of you. I will try everything you said and I will inform you if it worked since I am new in Märklin and I do not have much knowledge.

Peter, I think the interface hardware works well because my father used it with Basic and it worked like two or three years ago. Yesterday I could not check that the interface is working well because I think it was my own error. I will also try to check the wiring, but with the 6021 the system works well. The problems come when I try to control it by the interface connected to the control unit.

Dale, with that Labview screenshot you could not know the orders I tried to send with ASCII: Chr$(10) + Chr$(10); (the speed desired was 10 and the locomotive code is also 10).

Hi,

I have built my whole control system using LabVIEW. I used to have an Edits Pro Controller which should be compatible with the 6050. I have rewritten the whole thing to IB-Com lately, but I can send you an earlier version for Edits Pro if you send me your email address by PM.

Best regards,
Gregor