Rockwell Automation 1785-Lxxx Enhanced and Ethernet PLC-5 Programmable Controllers - Manual (Page 125)

Publication 1785-UM012D-EN-P - July 2005
Communicating with Extended-Local I/O 8-7
Calculating Block-Transfer Completion Time
You can calculate two types of block-transfer timing:
• worst-case calculation for the completion of all block-transfers
in the system
• the time to perform a block-transfer for any one block-transfer module
in the system
Calculating Worst-Case Completion Time
block-transfer duration (ms) = D R
D = 2E L + (0.1W) and
where:
E
= number of extended-local I/O 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
Calculating Completion Time for any One Block-Transfer
block-transfer duration (ms) = D R
D = [2E M + (0.1W)] and
where:
E
= number of extended-local I/O 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
This formula assumes:
block-transfer instructions are
consecutively placed in the logic program
block-transfer modules in the I/O chassis
are ready to perform when operations are
requested
R =
logic scan + housekeeping
logic scan
R = 1 (when D < logic scan time)
or
This formula assumes:
block-transfer instructions are
consecutively placed in the logic program
block-transfer modules in the I/O chassis
are ready to perform when operations are
requested
R =
logic scan + housekeeping
logic scan
R = 1 (when D < logic scan time)
or