FANUC Robotics America GFK-1535A - Manual (Page 46)

3-6 VersaMax™ System Genius® Network Interface Unit User's Manual – November 2000 GFK-1535A
3
Output Data Format
Each time the PLC or computer that controls the NIU has the bus communications
token, it sends fresh output data on the bus. Outputs for the NIU are sent in one
output data message, with all configured discrete outputs followed by all configured
analog outputs.
Output Data Message
(up to 128 bytes)
discrete outputs analog outputs
AQ starting reference data Q starting reference data
To
Station
⇐
Í Configured Q Length О Н Configured AQ Length
The data lengths are equal to the configured lengths of Q and AQ data selected for
the NIU (regardless of the host type or the amount of output data needed for the
modules physically present in the station). Either length may be zero.
When generating the output data message, a Series 90 bus controller automatically
places the Q data ahead of the AQ data. Other types of controllers must send an
output message consisting of the correct number of bytes of discrete output data
followed by the correct number of bytes of analog output data. The output data
format shown above is required by the NIU.
As soon as new output data is received, the NIU checks to be sure the data is error-
free and of the correct length. After verifying the accuracy of the data, the NIU puts
the data in its Q and AQ tables. Each discrete output module receives one byte of
data for every eight points. Each analog output module receives two bytes (one
word) for each analog channel.
Output Defaults
Except for outputs that have been previously forced, all other outputs are set to their
programmed defaults during the first Genius bus scan after powerup. The
previously-forced outputs are immediately set to their forced values.
If the NIU loses contact with its host for three successive bus scans or 1.2 seconds,
whichever occurs first, the NIU takes control of the outputs. The NIU sets output
data to the configured values. If the NIU loses contact with its host for 3 bus scans
or 1.2 seconds, and it has been configured in “Hot Standby” or “Duplex”
Redundancy mode, or if configured as a “BSM Controller”, or as “BSM present”,
the NIU operates as described in the Genius I/O System and Communications
Manual.