GEMTEQ I/O 4. GEMCAN I/O Scanner Configuration
If Port A/C is a Redundant Master,
then Port B/D must also be a
redundant Master and visa versa.
4 Change-Over
Master
4.2.4.2 Port Sub Mode ( Y )
When operating as a master, the GEMCAN I/O Scanner port may be operated in two sub-modes,
as detailed below in Table 4-5.
Table 4-5
GEMCAN I/O Scanner – Port Sub Mode
Port Sub
Mode
Description
0
Wait
At the end of the host controller ladder scan, if all the previous changed
output data has not been transmitted on the GEMCAN network then the
system waits until this is complete. A new set of output data is then
passed to the GEMCAN I/O Scanner module.
An updated set of input data is then read and a new ladder scan
commenced.
In this mode all output changes will be transmitted to the output modules
but a lengthening of the scan time may be observed, especially at low
baud rates.
1
NoWait
At the end of the host controller ladder scan, if all the previous output
data has been transmitted on the GEMCAN network, an updated set of
output data is passed to the GEMCAN I/O Scanner module. If all
previous output data has not been transmitted, then the system does not
wait but moves on to reading the input data.
A updated set of input data is always read at the end of the ladder scan
and a new ladder scan commenced.
In this mode output data is only passed to the GEMCAN I/O Scanner
module, to be transmitted on the GEMCAN network, as fast as the
network can take it. This may mean that fleeting outputs may be missed
but no extended scantimes should be seen.
If the system is operating at low baud rates and there is a lot of data to output, then it is
possible to observe long ladder scantimes which may affect other parts of the control system.
In this case it may be preferable to operate the master in NoWait mode.
4.2.5
Master Changeover Time (mS)
Module 1 (Port A Px+4, Port B Px+15) / Module 2 (Port C Px+33, Port D Px+44
)
Range
1 to 32000 mS
On a Change-over Master, this is the amount of time a given master will wait and expect to
see master Node Guard events on the network. If no such messages are observed then the
master will take mastership of the GEMCAN network.
Please refer to application note Appendix C.
GEMTEQ I/O Technical Manual (T2031En)
Rev.02 (10/10)
Page 4-5
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