I have an idea.
rodw: Can you make the bits from 0x6041 available as pins?
Then we can observe the bits during the home run.
If we know which bit is set when, the state machine could be set up accordingly.
But maybe we're overcomplicating things.
I took a look this afternoon and looked at various CIA drives. 0x6040 and 0x6041 are standardized. All CIA402-compatible drives use the same bits.
See here:
Bosh Rexroth CIA Status word
That means all we really need to do is find a suitable SCL code from Beckhoff or Siemens and rewrite it for Linuxcnc. For example, this one:
Code:
VAR
// PDO mapping inputs (from the drive)
wStatusword : WORD; // 0x6041
iActualMode : SINT; // 0x6060
// PDO mapping outputs (to the PLC)
wControlword : WORD; // 0x6040
iModeOfOp : SINT; // 0x6060
// Control / Monitoring
bStartHoming : BOOL; // Trigger
bHomingActive: BOOL; // Status
bHomed : BOOL; // Target reached
bError : BOOL; // Monitoring: Error
iState : INT := 0; // Step chain
// Monitoring: Timer
fbTimeout : TON;
END_VAR
// --- Read status bits from status word (0x6041) ---
// Bit 12: Homing process running / successful (depending on method)
// Bit 13: Homing error
// Bit 10: Target reached (often used during homing)
bHomingActive := (wStatusword.12); // Homing operation in progress
bHomed := (wStatusword.12) AND (wStatusword.10);
bError := (wStatusword.13); // Homing error
// --- Monitoring (timeout) ---
fbTimeout(IN := bHomingActive AND NOT bHomed, PT := T#10S);
// --- State machine for homing (CiA 402) ---
CASE iState OF
0: // Wait for start
IF bStartHoming AND NOT bError THEN
bStartHoming := FALSE;
iState := 10;
END_IF;
10: // Set mode of operation to “Homing” (6)
iModeOfOp := 6;
IF iActualMode = 6 THEN
iState := 20;
END_IF;
20: // Set drive to “Operation Enabled” (standard CiA402 state machine)
// Simple example: Set control word to 0x0F (Enable)
wControlword := 16#000F;
IF (wStatusword AND 16#006F) = 16#0027 THEN // Ready to operate
iState := 30;
END_IF;
30: // Start homing: Set bit 4 in control word (start homing procedure)
wControlword := 16#001F; // Bit 4 high, enable op
IF bHomingActive THEN
iState := 40;
END_IF;
IF fbTimeout.Q OR bError THEN iState := 999; END_IF; // Monitoring
40: // Wait for completion
IF bHomed THEN
wControlword := 16#000F; // Reset homing start bit
iState := 0;
END_IF;
IF fbTimeout.Q OR bError THEN iState := 999; END_IF; // Monitoring
999: // Error state
// Error handling: Cancel homing, set message
wControlword := 16#000F; // Stop
bError := TRUE;
IF NOT bStartHoming THEN iState := 0; bError := FALSE; END_IF;
END_CASE;
