The machine powers up and manual jog works, but the laptop and Fagor 8055 EPROM control will not synchronize or transfer a program. Treat this as a serial-link commissioning problem: prove the physical interface, cable conductors, computer port, matching communication settings, and transfer sequence in that order. Manual axis motion proves that parts of the CNC operate; it does not test the RS-232 path.
Transfer Function and Communication Boundary
The term communication here means transferring CNC program files through the serial interface. It does not mean that the laptop becomes a general-purpose motion controller. WinDNC acts as one endpoint, while the CNC remains responsible for program storage, interpretation, and machine operation.
An asynchronous serial transfer requires two active endpoints. Starting transmission in WinDNC alone is insufficient when the CNC is not in its receive function. Likewise, placing the CNC in receive mode does nothing until the computer sends data. This explains why an apparently connected system can wait indefinitely without reporting a clear fault.
- Identify the CNC function used to receive a program through the serial port.
- Identify the WinDNC command used to send a file to that configured connection.
- Do not begin with remote execution or machine movement. Commission file reception first.
Check 1: expect both endpoints to present complementary actions: receive at the CNC and send at the laptop. If either endpoint is configured for the opposite direction, correct the selected function before testing the wiring.
Serial Interface Identification
A DB9 connector identifies only the shell and contact count; it does not prove the signal assignment or whether the port behaves as data terminal equipment or data communications equipment. Two cable drawings can both be valid for different port roles. A straight-through cable and a crossed transmit/receive cable are not interchangeable.
Locate the serial-interface designation and pin assignment for the exact Fagor 8055 EPROM hardware. Then obtain the computer port or adapter pin assignment. Build the cable from signal names rather than matching pin numbers by appearance. At minimum, the transmit output of one endpoint must reach the receive input of the other, and the endpoints must share the specified signal reference. If the configured transfer uses hardware handshaking, its control lines must also follow the applicable diagram.
Disconnect both devices before continuity testing. Use a meter to map every installed conductor from one connector to the other and check for shorts between adjacent contacts and the connector shell. Record the mapping so that later troubleshooting does not depend on wire color or an unverified schematic.
Check 2: expect continuity only between contacts assigned by the selected signal-to-signal drawing, with no unintended contact-to-contact or contact-to-shell short. Do not proceed while the choice between the two cable schematics remains unresolved.
Computer Port and USB Adapter Isolation
A native RS-232 computer port provides the cleanest diagnostic baseline. A USB-to-serial adapter adds a driver, a virtual COM-port assignment, USB power behavior, and adapter-specific signal implementation. Any one of these can prevent communication even when WinDNC opens successfully. The reported setup used a DB9-to-USB adapter, so isolate that component early rather than changing several CNC settings around it.
- Use a laptop or desktop with a native serial port for the first test when one is available.
- If an adapter must be used, confirm that the operating system lists it without an error and note its assigned COM port.
- Select that same COM port in WinDNC. Close other software that may have opened the port.
- Reconnect the adapter to the same USB socket during commissioning so that an automatic COM-port reassignment does not invalidate the configuration.
Operating-system access controls can also interfere with legacy communication software. Windows 7 was specifically associated with I/O-port access trouble in this case. A native port does not correct a blocked or misaddressed software port, so verify the application can actually open the selected interface.
Check 3: expect the adapter or native serial device to appear as one usable COM port, and expect WinDNC to open that exact port without a busy, missing-port, driver, or access error.
Matched Communication Parameters
RS-232 defines electrical signaling, not a complete file-transfer configuration. Both endpoints must use the same character framing and flow-control method. Compare every value shown by the CNC communication page with the corresponding WinDNC connection fields. Do not guess missing values or change several parameters between tests.
| Setting | Required comparison | Typical mismatch result |
|---|---|---|
| Baud rate | CNC value equals WinDNC value | No readable transfer or corrupted characters |
| Data bits | Same character width at both endpoints | Rejected or altered characters |
| Parity | Same parity selection | Character errors or aborted reception |
| Stop bits | Same stop-bit selection | Intermittent or complete framing failure |
| Flow control | Same method, supported by the cable | Transfer never starts, pauses, or truncates |
| COM port | WinDNC selects the physical or virtual port in use | No traffic reaches the cable |
If the CNC displays a configured value, copy it into WinDNC before altering the control. This preserves the machine configuration while establishing a known baseline. Where a field name differs between the two interfaces, compare its function rather than assuming similarly positioned menu items are equivalent.
Check 4: expect a field-by-field match between the CNC serial configuration and WinDNC, including the flow-control selection. Record the settings before the first transfer attempt.
Coordinated Receive-and-Send Procedure
Use a small, known-valid program already accepted by this CNC model. A short file reduces the time needed to distinguish a link failure from buffer handling, file size, or program-format trouble. Preserve the machine's existing programs before receiving a file that could reuse an occupied program identifier.
- Connect the verified cable with both endpoints idle.
- Open WinDNC and select the commissioned COM port and matching serial parameters.
- Select the CNC operation for receiving a program through the serial interface.
- Confirm that the CNC indicates a waiting or receive state.
- In WinDNC, select the known-valid test file and start the send operation.
- Wait for both endpoints to finish before leaving receive mode or disconnecting the cable.
If nothing starts, recheck port selection, transmit/receive crossing, and the handshake method. If characters arrive but are unreadable, recheck baud rate, parity, data bits, stop bits, and signal reference. If a transfer starts and then stops, inspect flow-control wiring and configuration before blaming the program content. If the full file arrives but the CNC rejects it, move the investigation to file syntax, delimiters, and CNC program format.
Check 5: expect WinDNC to complete transmission and the CNC to leave its waiting state with a received program present. A file listed with missing lines or altered characters is not a successful transfer.
End-to-End Verification
- Physical check: expect the recorded cable map to match the selected Fagor-to-computer signal diagram.
- Port check: expect WinDNC to open the same COM port assigned by the operating system.
- Configuration check: expect every serial parameter and the flow-control method to match at both endpoints.
- Integrity check: expect the received program identifier, line order, and content to match the transmitted file.
- Reverse-path check: where the configured CNC transfer function provides transmission to the computer, send a known program from the CNC and compare the saved result with the source.
Perform any machine execution only after reviewing the received program on the control and applying the machine's normal safe proving procedure. File-transfer success proves data integrity; it does not prove that the program is safe for the tooling, workholding, axis limits, or current machine state.
Frequently Asked Questions
Why does my Fagor 8055 jog but not communicate?
Jog operation and RS-232 communication use different subsystems. Prove the serial cable, COM port, matched framing parameters, flow control, and coordinated receive/send sequence independently.
Why does WinDNC wait without transferring a file?
The CNC may not be in its serial receive function, or WinDNC may have opened the wrong COM port. Put the CNC into its waiting receive state first, then start the send operation from WinDNC.
Why does a USB-to-serial adapter fail with the Fagor 8055?
The adapter adds driver, virtual-port, and signal-control dependencies. Establish the first working link with a native RS-232 port when available; otherwise verify the adapter's driver state, COM-port assignment, and handshake-line support.
Why are there two different DB9 cable schematics?
They may target different endpoint roles or handshake methods. Select the drawing by signal names, then meter the finished cable for transmit-to-receive routing, the specified signal reference, required handshake conductors, and shorts.
Why does the transfer finish but the CNC program look wrong?
Unreadable or altered characters point to mismatched baud rate or character framing; truncation points to flow control. Repeat the final integrity check and expect the received identifier, line order, and complete file content to match the WinDNC source.