FANUC Robotics America GFK-1535A - Manual (Page 44)

3-4 VersaMax™ System Genius® Network Interface Unit User's Manual – November 2000 GFK-1535A
3
Data Transfer Between the NIU and the Bus
Each bus scan, an NIU exchanges the following data with the bus:
T It sends an input message with up to 128 bytes of discrete and/or analog inputs.
T It receives an output message with up to 128 bytes of discrete and/or analog
outputs.
The exact length of these messages is determined by the network I/O map
configured for the NIU.
Communications on the Genius Bus
After the NIU completes a successful login on the bus, it starts sending input data
and accepting output data on the bus. The NIU communicates on the bus
repetitively and asynchronously relative to the I/O scan. When the NIU receives the
bus communications token, it sends the most recent data from its I and AI
memories.
NIU Memories
I
AI
Q
AQ
BUS
The NIU receives new outputs from the bus when the PLC or computer bus
controller has the communications token. The NIU places these outputs its Q and
AQ output tables.
NIU Memories
I
AI
Q
AQ
BUS
These outputs are then passed to the devices in the station on the NIU's next internal
I/O scan.