PLSY Operand-Size Constraint
PLSY accepts WORD registers for both the commanded frequency and pulse count. Treat operand capacity as the first selection criterion: a command that requires values beyond the applicable WORD representation cannot be expressed directly with PLSY.
Selecting PLSY or DPLSY
| Instruction | Frequency operand | Pulse-count operand | Selection rule |
|---|---|---|---|
| PLSY | WORD | WORD | Use when both required values fit the PLC's applicable WORD representation. |
| DPLSY | DWORD | DWORD | Use when either required decimal value needs DWORD capacity. |
The evidence does not identify the PLC model, operand signedness, instruction syntax, or numeric ranges. Confirm those details in the programming reference for the installed controller before entering boundary values.
Configuration Procedure
- Determine the required frequency and total pulse count for the motion command.
- Check whether both values fit the controller's documented WORD representation. If they do, use PLSY; if either value requires DWORD capacity, use DPLSY.
- Check the controller's documented maximum high-speed-output frequency. A frequency command above the output capability is limited to the maximum frequency supported by the PLC.
Verification and Diagnostics
Monitor the frequency and pulse-count operands online to confirm that the program writes the intended values without truncation or representation errors. Then measure or monitor the physical pulse output and compare it with the controller's documented maximum. If a large command does not produce the requested frequency, distinguish an operand-size problem from the PLC's high-speed-output frequency limit.
FAQ
Why can PLSY not accept my required pulse count?
PLSY uses WORD operands for frequency and pulse count. Select DPLSY when either required value needs DWORD capacity.
Does DPLSY use DWORD values for both frequency and pulses?
Yes. The supplied evidence identifies both the frequency and pulse-count operands of DPLSY as DWORD values.
What happens if the PLSY frequency command is too high?
The PLC limits its high-speed output to the maximum frequency the hardware supports. Verify that limit in the installed controller's documentation because no model-specific value is provided.