72
Timing Considerations
Section 3-3
3-3-2
Turnaround Time
Turnaround time (TAT) is the elapsed time from the retrieval of a command by
the PC until the data has been read from or written to the Data Carrier. Turn-
around time can be calculated as follows:
TAT = Coefficient x PC scan time + Command processing time (+ Remote I/O
communication time, if applicable)
Coefficient: Differs according to the number of bytes to be read/written and
the I/O refresh time.
PC scan time: The time required by the CPU to scan the program, refresh the
I/O area, etc. Determine this value by referring to
Coefficient Values
below.
Command processing time: The time required to process the communication
between the ID Sensor Unit and the Data Carrier. Determine this value by
referring to
Section 3-3-1 Command Processing Time
.
Remote I/O communication time: additional time required when the ID Sensor
Unit is mounted to a Remote I/O Slave Rack. If the ID Sensor Unit is not
mounted to a Remote I/O Slave Rack, this time is zero.
Coefficient Values (per execution of a single command)
1,2,3...
1.
Write (Auto Write) command
Coefficient (min) = [(number of bytes of data to be trans 8) / 40] + 3
(Round up to next whole number.)
Coefficient (max) = Coefficient (min) + 2
2.
Read (Auto Read) command
Coefficient (min) = (number of bytes of data to be transferred / 40) + 5
(Round up to next whole number.)
Coefficient (max) = Coefficient (min) + 2
3.
Clear-all command
Coefficient (min) = 4
Coefficient (max) = 6
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