Rockwell Automation 1756-L55M12, Руководство по выбору

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1756-SG001G-EN-P — March 2004
How ControlLogix
Modules Operate In a ControlLogix system, I/O updates occur asynchronous to the execution of logic.
This lets your application receive updated data as soon as possible. If your application
needs synchronous I/O updates, use the synchronous copy (CPS) instruction to buffer
I/O data at the beginning of each scan.
Module Type Placement Operation
digital input
local chassis
The RPI specifies the rate at which a module multicasts its data. The time ranges from 200
microseconds to 750 milliseconds. When the specified time frame elapses, the module will multicast
data (also called cyclic data exchange).
If a change of state (COS) does not occur within the RPI timeframe, the module multicasts data at the
rate specified by the RPI.
Because the RPI and COS functions are asynchronous to the logic scan, it is possible for an input to
change state during program scan execution. If this is a concern, buffer input data so your logic has a
stable copy of data during its scan. Use the Synchronous Copy (CPS) instruction to copy the input
data from your input tags to another structure and use the data from that structure.
remote chassis
The RPI and COS values still define when the module multicasts data within its own chassis, but only
the value of the RPI determines when the owner controller receives the data over the network.
When an RPI value is specified for an input module in a remote chassis, in addition to instructing the
module to multicast data within its own chassis, the RPI also reserves a spot in the stream of data
flowing across the control network. The timing of this reserved spot may or may not coincide with the
exact value of the RPI, but the owner-controller will receive data at least as often as the specified RPI.
digital output
local chassis
If the module resides in the same chassis as the owner-controller, the module receives the data
almost immediately after the owner-controller sends it. Data is sent after all the programs within each
task have completed executing.
remote chassis
If an output module resides in a chassis other than that of the owner-controller (i.e. a remote chassis
connected via ControlNet or Ethernet/IP), the owner-controller sends data to the output module only
at the RPI rate.
The RPI also reserves a spot in the stream of data flowing across the control network. The timing of
this reserved spot may or may not coincide with the exact value of the RPI, but the output module
receives data at least as often as the specified RPI.
analog input
local chassis
The RTS value specifies when the module scans its channels and multicasts the data (update the input
data buffer then multicast). The RPI value specifies when the module multicasts the current contents
of the input data buffer without scanning (updating) the channels.
The module resets the RPI timer each time an RTS transfer occurs. If the RTS value is less than or
equal to the RPI value, each multicast of data from the module has newly updated channel data. The
module only multicasts at the RTS rate.
If the RTS value is greater than the RPI, the module multicasts at both the RTS rate and the RPI rate.
remote chassis
The RPI and RTS rates still define when the module multicasts data within its own chassis, but only
the RPI value determines when the owner-controller receives the data over the network.
The RPI also reserves a spot in the stream of data flowing across the control network. The timing of
this reserved spot may or may not coincide with the exact value of the RPI, but the controller receives
data at least as often as the specified RPI.
analog output
local chassis
The RPI value specifies when the owner-controller broadcasts output data to the module. If the
module resides in the same chassis as the owner-controller, the module receives the data almost
immediately after the owner-controller sends it.
remote chassis
If an output module resides in a chassis other than that of the owner-controller (i.e. a remote chassis
connected via ControlNet or Ethernet/IP), the owner-controller sends data to the output module only
at the RPI rate.
The RPI also reserves a spot in the stream of data flowing across the control network. The timing of
this reserved spot may or may not coincide with the exact value of the RPI, but the output module
receives data at least as often as the specified RPI.