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12.7.7
Pre-reading start function
The "pre-reading start function" does not output pulses while the execution prohibition flag is ON if a positioning start
request is given with the execution prohibition flag ON, and starts outputting pulses within 1.3ms after OFF of the
execution prohibition flag is detected. The positioning start request is given when the axis is in a standby status, and
the execution prohibition flag is turned OFF at the axis operating timing. This shortens the virtual start time. The LD75
normally takes 1.5 to 2.0ms from when it receives a positioning start request until it starts pulse output (start time).
Some systems often need the start time to be shortened. This "pre-reading start function" can improve the tact time of
the system.
The "pre-reading start function" will be explained below.
• Control details
• Control precautions
• Program example
(1) Control details
The pre-reading start function is performed by turning ON the positioning start signal [Y10, Y11, Y12, Y13] with
the execution prohibition flag [Y14, Y15, Y16, Y17] ON, or by executing the dedicated instruction (ZP.PSTRT1,
ZP.PSTRT2, ZP.PSTRT3, ZP.PSTRT4). However, if positioning is started with the execution prohibition flag ON,
the positioning data is analyzed but pulse output is not provided. While the execution prohibition flag is ON,
"[Md.26] Axis operation status" remains unchanged from "5: Analyzing". Pulse output starts within 1.3ms after the
execution prohibition flag [Y14, Y15, Y16, Y17] has turned OFF, and "[Md.26] Axis operation status" changes to
the status (e.g. "Position control", "Speed control") that matches the control system.
V
Positioning start
ON
signal
[Y10,Y11,Y12,Y13]
Execution
OFF
prohibition flag
[Y14,Y15,Y16,Y17]
ON
BUSY signal
[XC,XD,XE,XF]
Axis operation
Md.26
Position control
status
598
Start time
ON
OFF
ON
OFF
Positioning data
analysis
Standby
Positioning start timing
OFF
Ta
1.3ms or less
Execution prohibition flag OFF waiting
Analyzing
t
ON
Position control
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