ProSoft Technology MVI56E-GSC/ GSCXT - Manual (Page 81)

MVI56E-GSC ♦ CompactLogix or MicroLogix Platform Reference
Enhanced Generic ASCII Serial Communication Module User Manual
ProSoft Technology, Inc. Page 81 of 140
May 9, 2014
As shown in the illustration above, all data transferred between the module and
the processor over the backplane is through the input and output images. Ladder
logic must be written in the ControlLogix processor to interface the input and
output image data with data defined in the Controller Tags. Your ladder logic
must handle and interpret all data received on the application ports and
transferred into the input image. You must also construct messages to be
transferred out of the application ports by building the messages in the
appropriate controller tags for transfer to the output image of the module.
4.2.2 Data Flow between MVI56E-GSC Module and ControlLogix
Processor
The following topics describe the flow of data between the two pieces of
hardware (ControlLogix processor and MVI56E-GSC module) and other devices
attached to the application ports. Each application port on the module is
configured independently to interface with serial communication devices. The
sections below show the three possible types of communication devices that can
be attached to the application ports: write-only, read-only and read-write.
Write-Only Devices
Write-only devices are those that only send data to the module. An example of
this type of device is a barcode reader which has been configured to only send
data and is not expecting to receive data.
In this situation, the application port on the MVI56E-GSC module will never have
to transmit data. All data received from the barcode reader will be passed from
the module to the ControlLogix processor through the module’s input image.
Ladder logic in the processor must handle the data received from the module.
The output image on the module will only be used to inform the module when the
input image has been processed. This is accomplished by copying the Byte 499
in the input image to Byte 0 of the output image.
The data flow diagram for a write-only device is shown below: