GE GFK-0825F Input Data Sent by the Bus Interface Unit

4-10 Field Control™ Genius® Bus Interface Unit User’s Manual – October 1999 GFK-0825F
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Input Data Sent by the Bus Interface Unit
When the Bus Interface Unit takes its turn on the bus, it sends one input data message containing
the latest values for all configured discrete inputs followed by all configured analog inputs.
Because they are broadcast (like all Genius inputs), they can be obtained by any Bus Controller on
the bus.
Input Data Message
(up to 128 bytes)
discrete inputs analog inputs
Configured I Length Configured AI Length
AI starting reference dataI starting reference data
T
o CPU
The data lengths are equal to the configured length s of I an d AI da ta selected for the Bus Inter fa ce
Unit (regardless of the host CPU type or the actual amount of output data needed for the modules
physically present in the station). Either length may be zero.
The discrete inputs appear in the input message in the same sequence as their assigned input
references. Each discrete input module occupies one byte per eight circuits.
The analog inputs are als o in the same sequence as their assi gned input references. Each an al og
input module occupies two byt es (one word) for each anal og ch an n el.
The Bus Interface Unit sends this data from its internal I and AI memories, beginning at the start
locations selected during station configuration.
Input Defaults
When configuring input modules, either a default state or hold last state can be selected. If an input
module is removed or fails to operate correctly, the chosen state is substituted for actual input data.
A diagnostic message is provided to indicate loss of module. Forced input data is not affected.
I/O Data Handling by Hos t
How the host handles input data from the Bus Interface Unit depends on the host type:
A Series 90-70 PLC places the data in the %I and %AI references selected during PLC
configuration. These must be the same references selected during Bus Interface Unit
configuration.
A Series Six or Series Five PLC p la ces the data into I/O table or r egister memory. A
beginning a d dress in Serie s S ix or Series Fi ve I/O Table mem ory can be enter ed during stati on
configuration.
A host computer with a PCIM modu l e places the data into the in put ta ble segment that
corresponds to the seria l bus address (Device Number ) of th e Bus Interface Unit.