u/LorenzoCM757

Hello everyone,

I'm fighting with a data transfer issue on a Mecof milling machine equipped with a Heidenhain TNC 430 control. I am consistently getting a [NO DIR] error on the machine when trying to access the PC via RS-422 or RS-232 using both TNCserver and TNCremo.

Here are the technical details and what I have already tried. Any help from Heidenhain veterans would be hugely appreciated.

1. The Hardware Setup:

• Machine: Mecof with Heidenhain LE 426/430.
• PC 1: Desktop running Windows XP with a native, physical COM1 port.
• PC 2: Laptop running Windows 11 with USB-to-RS232 adapters.
• Converter: Sintechi RS-232 to RS-422/485 passive terminal block converter. It is externally powered with 12V DC.
• Software: TNCserver / TNCremo.

2. The Port & Wiring (The Mystery):

• Outside the electrical cabinet, there is a factory DB15 port labeled "Program Loading".
• I traced this cable inside the cabinet: it is physically connected to the X22 port on the Heidenhain logic unit.
• Electrical Verification: I measured the voltage on the DB15 pins while the machine was on. Between Pin 2 (GND) and Pin 4, I get 0.9V DC at rest. This confirms it is an active RS-422 differential line, not RS-232.
• Pinout used on DB15: * Pin 2 = GND
  • Pin 3 = TX+
  • Pin 4 = TX-
  • Pin 5 = RX+
  • Pin 6 = RX-

3. What I have already tried (Troubleshooting):

• Software Settings: PC set to LSV-2, 9600 Baud, 8-N-1. Machine MOD menu set to RS-422, LSV2, 9600 Baud.
• Handshake: Set to SOFTWARE (Xon/Xoff) or NONE on the PC. (The machine MOD menu for RS-422 doesn't even show an handshake option).
• Windows XP COM1: I disabled the FIFO buffers entirely in the advanced COM1 device manager settings.
• Polarity Swapping: I swapped the TX+/TX- and RX+/RX- wires on the Sintechi converter to account for incorrect Chinese labeling. Still [NO DIR].
• RS-232 attempt: I also tried connecting a custom Null-Modem cable (with 4-5 and 6-8-20 bridges) to the X21 port, but it didn't work either. Tried all baud rates, FE protocol, different parities, etc.

My questions for the experts:

1. Since the factory "Program Loading" cable goes to X22, are the DB15 pins (2, 3, 4, 5, 6) exactly correct for the Heidenhain RS-422 TX/RX pairs on this specific port? Do I need to change a specific Machine Parameter (MP) to enable data transfer through X22?
2. Right next to it, the X21 port is empty. Is X21 the actual RS-232 port? I tried connecting a standard Null-Modem cable (bridged 4-5 and 6-8-20) to X21, but got "Interface not ready" / no connection regardless of baud rate or FE/LSV2 protocols. If X21 is the 232, what is the exact trick/pinout to make it work?
3. Has anyone successfully used one of these cheap active/passive Sintechi RS422 converters on a TNC 430?

Thanks in advance for your time!