3
Remote I/O Scanner User’s Manual – July 199248
Outputs from the Host to a Remote Drop
Each time the host’s Bus Controller has the bus communications token, it sends any
outputs it has received from the CPU to the devices on the bus. Outputs for the
Remote I/O Scanner 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
Configured %Q Length Configured %AQ Length
%AQ starting reference data%Q starting reference data
To
Remote
Drop
The lengths of each portion are equal to the configured lengths of %Q and %AQ data
selected for the Remote I/O Scanner (regardless of the host CPU type or the actual
amount of output data needed for the modules physically present in the remote drop).
Either length may be zero.
The Series 90–70 Bus Controller automatically places the %Q data ahead of the %AQ
data, in accordance with the configuration supplied to the host PLC for the remote
drop. Other PLCs and computers need to prearrange the data in the order expected
by the remote drop. Each discrete output module will receive one byte of data for each
eight circuits. Each analog output module will receive two bytes (one word) for each
analog channel.
As soon as new output data is received, the Remote I/O Scanner checks it to be sure the
data is error–free and of the cor rect length. The length must match the combined
lengths of the discrete output data and analog output data that have been configured
for the Remote I/O Scanner. After verifying the accuracy of the data, the scanner puts
the data in the %Q and %AQ tables, and begins passing it to the output modules in the
remote drop.
Output Defaults
On powerup, all outputs are turned off (analogs go to zero), except those inputs and
outputs which had previously been forced––they go immediately to their forced state
or value.
If CPU communications are lost for 3 bus scans, all outputs that are not presently
forced will either default or hold their last state, as configured using the Logicmaster
90–70 software. If all configuration for a remote drop is done with a Genius
Hand–held Monitor, this selection cannot be made and all outputs will default to Off
(or 0 for analogs).