Siemens SIMATIC TIWAY 1 - Manual (Page 41)

OPERATION AND APPLICATION
UNILINK HOST ADAPTER 2–31
USER MANUAL
2.10.1.2 Repetitive and Non-Repetitive Macros
You specify in each macro definition whether the macro should be issued one
time or repeated at regular time intervals. Non-repetitive macros are issued
once and collect one macro response, functioning much like a direct command.
To reissue the non-repetitive macro, your applications software only needs to
send the ENABLE/DISABLE MACRO EXECUTION command to enable it,
saving the host-to-adapter communications overhead of sending the Primitive
data again.
Repetitive macros are issued at the specified time intervals with each new
macro response replacing the previous response. The macro will be repeated
until your applications software sends the ENABLE/DISABLE MACRO
EXECUTION command to disable it. Both repetitive and non-repetitive macros
are scheduled for processing by the HIU function.
The HIU function schedules the requests in the following order:
1. Direct commands for a single secondary device
2. Direct commands for multiple secondary devices
3. Non-repetitive macros
4. Repetitive macros
The HIU function queues all requests except the direct commands for single
secondaries. A single secondary direct command is given a higher priority and
will be sent to the NM function before any of the queued requests. This priority
scheme prevents the repetitive macros from using the entire network
bandwidth.
When the ENABLE/DISABLE MACRO EXECUTION command code is issued,
the non-repetitive macros will be sent in the order listed in the command
parameters. The provides a method for defining your own execution priority for
the non-repetitive macros. Repetitive macros can be used for background data
acquisition, freeing the host computer application even further. Each new
repetitive macro response is compared to its previous response and if a
difference is detected, the exception flag for that macro is set. The host computer
application can check the state of the exception flag and act accordingly without
the overhead of collecting and comparing the macro responses itself. A Freeze
Exception option can be specified when defining the repetitive macros. This
option will disable the macro execution when the exception is detected, and
freeze the data that caused the exception.