Rockwell Automation 1785-Vx0B, D17856.5.9 PLC-5 VME VMEbus Programmable Controllers User Manual - Manual (Page 120)

Performance and Theory of Operations
Chapter 7
7-15
Block-transfer duration is the time interval between the enabling of the
block-transfer instruction and the receipt of the done bit. The following
example and formulas make two assumptions:
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
The following example sets up a system and provides two formulas for
calculating block-transfer timing. The first formula is a worst-case
calculation for the completion of all block-transfers in the system. The
second formula enables you to calculate the time to perform a
block-transfer for any one block-transfer module in the system.
For example, a PLC-5/V40L may have three extended-local I/O chassis
connected to channel 2. The first chassis contains two block-transfer
modules; the second chassis contains one block-transfer module; and the
third chassis does not contain block-transfer modules. It takes the logic
scan 15 ms to complete; it takes housekeeping approximately 6 ms to
complete (as calculated in the formula on page 7-13). The longest
block-transfer request is 20 words.
PLC-5/V40L
1771-ALX
Adapter 1771-ALX
Adapter 1771-ALX
Adapter
Extended-Local I/O Chassis 1 Extended-Local I/O Chassis 2 Extended-Local I/O Chassis 3
Two BT One BT No BT
Module Modules Modules
Extended-Local I/O Link 10818 I
Channel 2
Module Module Module
Processor