Siemens SIMATIC TIWAY 1 - Manual (Page 94)

HOST COMMAND SET REFERENCE
UNILINK HOST ADAPTER 5–9
USER MANUAL
5.3.2 Broadcast Network Data Transfer — 02
The BROADCAST NETWORK DATA TRANSFER command sends the
Primitive data to all online secondary devices. The secondary device log
contains only those secondary devices in the network that are online. However,
this type of information transfer does not use the full TIWAY I HDLC integrity
checks to ensure message delivery.
If the adapter is configured as an MHIU in EHA mode, the host applications
software must issue a POLL command for each secondary device to collect the
responses or some responses may be lost. In any other configuration, you should
include a data element that is set in the secondary with the broadcast and
checked by the host applications software by sending a SEND NETWORK
DATA command to determine if the broadcast message was received. The data
element can also be checked by the secondary devices program to cause it to
perform a programmed process. This function can be more efficiently handled
in non-MHIU/EHA networks by using macros for data acquisition.
NOTE
Before the data is broadcast, all pending TIWAY I
I–Frames from all HIUs will be processed. Then no
further directives will be processed until the
broadcast completes. This could have a serious
impact on the response time for normal network
operations and should be used carefully.
The following are typical uses for this command.
D Time synchronization for all secondary devices. This could be used to
signal all secondaries to reset their counters at the beginning of a
production period.
D Data collection via a snapshot read. The broadcast could signal the
secondaries to move data to a designated area in the secondary device
which will be retrieved later with a POLL or SEND NETWORK DATA
command.