ProSoft Technology MVI56-AFC - Manual (Page 163)

MVI56-AFC ♦ ControlLogix Platform MVI56-AFC Backplane Communication
Liquid and Gas Flow Computer User Manual
ProSoft Technology, Inc. Page 163 of 316
February 25, 2011
Sentinel & Anchor (Transaction Number)
In order to allow the AFC to tell each Output Block Array apart, a unique
Transaction Identifier number is assigned to each transmit block. This
Transaction Identifier number is assigned to the top and bottom elements of the
transaction block to ensure data transfer integrity. The top transaction identifier is
called the Transaction Number Sentinel and the bottom transaction identifier is
called the Transaction Number Anchor.
Output Block Length
The element immediately following the sentinel contains the length of the data
portion, not including the sentinel, the anchor, or the Output Block Length
element itself; hence its maximum value is 245. If the output data block you
configured is less than 245 elements, unused elements between the end of the
data block and the anchor are ignored on output (to the AFC) and returned as
zero on input (from the AFC).