Reference MVI94-GSC-E
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FLEX Platform
User Manual
Generic ASCII Comunication Module
ProSoft Technology, Inc.
Page 45 of 60
July 6, 2009
Read-Only Devices
Read-Only devices are those that only receive data from the module. An
example of this type of device is a printer. The printer will generate output or be
controlled based on the data it receives on its communication port. Ladder logic
is used to construct the write blocks to be sent to the module. When the module
receives a new write block containing data, it will transmit the data out the port.
The Block Sequence Number used in the write block (output image) should be
the one received on the last read block (input image). The data flow diagram for
a read-only device is shown below:
Before data is transmitted in the write block, the ladder logic should insure that
the port is not busy sending the previous write message. The Port 2 transmit
state returned in each status block should be monitored to determine the state of
the port. If the Port 2 transmit state has a value other than zero, the port is busy.
If the Port 2 transmit state has a value of zero, the port is ready for a new
message to transmit.
