Rockwell Automation 1785-Vx0B, D17856.5.9 PLC-5 VME VMEbus Programmable Controllers User Manual User Manual
Page 121
Performance and Theory of Operations
Chapter 7
7-16
Formula 1—Worst-case time to complete all block-transfers in
extended-local I/O system where block-transfer duration (in ms) = D x R
D =
2
E
x
L
+
(0.1
W)
Where:
Is the:
E
number of extended-local chassis with block-transfer modules
L
largest number of block-transfer modules in any extended-local I/O chassis
W
number of words in the longest block-transfer request
D
(ms)
=
(2
x
2)
x
(2)
+
(0.1
x
20
)
or
D
=
10
ms
R
=
1
(when
D
<
logic
scan
time)
OR
R
=
Logic
Scan
+
Housekeeping
------------------------
Logic
Scan
In this example,
R
= 1
(because the value of D (10 ms) < 15 ms logic scan time)
block-transfer duration (ms) = 10 x 1 or 10 ms
The block-transfer duration shown above does not affect logic scan time.
This transfer of data occurs concurrent with execution of program logic.
Formula 2—Time for any one block-transfer in extended-local I/O system
(calculate for chassis 2 with block-transfer request of 20 words) where
block-transfer duration (in ms) = D x R
D (ms) = 2C x M + (0.1W)
Where:
Is the:
C
number of extended-local chassis with 1771-ALX adapter modules
and block-transfer modules
M
number of block-transfer modules in the chassis of the module
being calculated
W
number of words in block-transfer request being calculated
D
(ms)
=
(2
x
2)
x
(1)
+
(0.1
x
20
)
or
D
=
6
ms
R
=
1
(when
D
<
logic
scan
time)
OR
R
=
Logic
Scan
+
Housekeeping
------------------------
Logic
Scan