Resolving HOME Command Buffer-Open Polling Failures

The PC HMI starts the X-Y-Y′ homing program, then receives Buffer is Open when it tries to read P50. The homing motion can still finish correctly; the failed poll means the controller’s ASCII command interpreter remains in program-entry mode when the query arrives. Treat buffer closure, motion execution, and status polling as three separate commissioning steps.

Command-path prerequisites

1. Identify every client that can write to the controller’s command interface: the PC HMI, PWIN terminal, download utility, and any background service. Permit only one outstanding ASCII transaction per command channel.
2. Before anything else, confirm that the stored program is closed. Send a standalone CLOSE through the same command path used for OPEN PROG 101 CLEAR, then read a harmless controller variable. Do not move on until the read returns a value rather than Buffer is Open.
3. Confirm the program-launch transaction receives its normal acknowledgement before starting the P50 poll. Do not concatenate program editing, program launch, and variable reads into one unverified character stream.

OPEN PROG 101 CLEAR selects and clears a program buffer so subsequent text is stored as program content. CLOSE returns the command interpreter to immediate-command mode. A P50 request sent before that transition can be parsed as attempted program text instead of a read request. Manually entering CLOSE restores polling because it corrects the parser state; it does not prove that the HOME motion itself failed.

Program download closure

1. Download the definition beginning with OPEN PROG 101 CLEAR.
2. Transmit the entire motion program without inserting HMI polls into the download stream.
3. Transmit the final CLOSE as a separate command and wait for its acknowledgement.
4. Read back a known variable before allowing the HMI to launch the program. This read is the acceptance test for buffer closure.

Place the download operation in a commissioning or maintenance state, not in the normal homing cycle. The CLOSE shown after the program body closes the definition buffer during download; it is not a runtime statement reached after homing. Repeatedly downloading the program immediately before execution creates a race in which the HMI can begin polling while the controller still accepts program text.

If multiple software components share the controller, protect the complete open-write-close exchange with one command-channel lock. Also log the transmitted command, acknowledgement, and timestamp. The required check is simple: after every download, an immediate read of P50 must succeed before program execution begins.

Homing-stage configuration

The routine contains three distinct motion stages. Commission and verify them separately before relying on the final completion bit.

The final HOME1..3 changes capture control, direction/speed, and offsets; it is not a duplicate of the first pass. Removing it shortens the transaction window and changes the established home result, so disappearance of the polling symptom does not identify that command as the buffer-opening operation.

The routine temporarily kills one gantry motor with COMMAND"#3k" or COMMAND"#2K" while its partner clears a limit, then re-enables it with COMMAND"#3J/" or COMMAND"#2J/". Test these branches at reduced machine risk and confirm both motors are enabled before either simultaneous HOME1..3 command.

HMI launch and polling handshake

1. Set P_HOMING_ROUTINE_COMPLETE, identified as P50, to 0 before starting motion.
2. Launch the already stored motion program using the controller’s normal run operation. Wait for the launch acknowledgement before issuing another ASCII command.
3. Poll P50 with one request outstanding at a time. Treat Buffer is Open as a communications-state fault, not as a value of P50.
4. Continue only when the response is a valid value. A returned 1 indicates that execution reached the assignment after the final HOME1..3.

The program sets P_MOTOR1_HOME_STATUS, P_MOTOR2_HOME_STATUS, and P_MOTOR3_HOME_STATUS to 1 at entry, then changes all three to 0 before setting P50=1. Those names do not define their polarity; commission the HMI labels against observed program execution rather than assuming that 1 means homed.

Verify that the controller does not execute the P50=1 assignment until all three axes have completed the final HOME operation. If program execution can advance while motion remains active, gate P50 with the controller’s documented home-complete and stopped conditions.

Branch and recovery checks

The line IF (ESTOP_Button=1) conflicts with the comment stating that an active E-stop must prevent homing. Determine the actual input polarity from the live variable and machine wiring. With the safety condition active, the program must take the non-homing branch and leave P50=0. With the safety condition healthy, it must enter the homing sequence.

1. On Buffer is Open, stop issuing repeated polls so they cannot add traffic to the wrong parser state.
2. Record whether a download was active and which client last sent OPEN, CLOSE, or the run request.
3. Send CLOSE only when no legitimate program download remains in progress.
4. Read P50 again. If the read succeeds, correct the missing acknowledgement, channel lock, or download/run sequencing that left the buffer open.

Do not use automatic, unconditional CLOSE commands as the normal polling strategy. They can terminate an intentional edit and hide the client that broke transaction ownership.

End-to-end verification

1. Power or reset the command session as required by the commissioning procedure, then download Program 101 through one open-write-close transaction.
2. Confirm an immediate read of P50 succeeds while the program is idle.
3. Run each active-limit clearing branch and verify that the killed gantry motor is re-enabled.
4. Run the first and final HOME1..3 stages. Confirm the configured capture controls and offsets are active for the intended stage.
5. During motion, poll P50 repeatedly and verify that every reply is a valid value, with no Buffer is Open response.
6. At completion, confirm P50=1, all three motor status variables are 0, limits are restored with I124/I224/I324=$8001, and the final software-limit settings have been written.

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