Rockwell Automation 1794-VHSC 1794 FLEX I/O Very High Speed Counter Module User Manual - Manual (Page 38)

30 Rockwell Automation Publication 1794-UM010D-EN-E - July 2013
Communicate With Your Module
Scheduled Data-Transfer
Scheduled data transfer:
• is continuous
• is asynchronous to the ladder-logic program scan
• occurs at the actual rate displayed in the Actual Packet Interval field on the
programming software I/O mapping (monitor) screen
Unscheduled Data-Transfer
Unscheduled operations include:
• unscheduled non-discrete I/O data transfers — through I/O transfer
instructions
• peer-to-peer messaging — through Message (MSG) instructions
• messaging from programming devices
Unscheduled messaging on an EtherNet/IP network is non-deterministic. Your
application and your configuration — number of nodes, application program,
NUT, amount of scheduled bandwidth used, and so on — determine how much
time there is for unscheduled messaging.
Module I/O Mapping
The I/O map for the 1794-VHSC module is divided into read words and write
words. Read words consist of input and status words, and write words consist of
output and configuration words. The number of read words or write words can
be 0 or more. The length of each I/O modules read words and write words vary in
size depending on module complexity. Each I/O module will support at least 1
input word or 1 output word. Status and configuration are optional, depending
on the module. The 1794-VHSC module has 9 input words, no status words, 4
output words and 56 configuration words.
Application of New Configurations
When a configuration is sent to the 1794-VHSC module, it is checked for
consistency before being applied. If an error is found in the configuration, the PE
bit (input word 8, bit 15) is asserted and the module locally retains its previous
configuration. To isolate any problems an improperly configured module may
have, the user application program (ladder program, for instance) should monitor
this error.