Siemens SIMATIC TIWAY 1 - Manual (Page 69)

CONFIGURING THE HOST COMPUTER PORT
UNILINK HOST ADAPTER 3–11
USER MANUAL
BDLC Host Command
BDLC Host Command
RR, “Poll”
RR, “Poll”
RR, “Message Received”
RR, “Message Received”
First Network Response
Second Network Response
Host
Computer
UNILINK
Host
Adapter
Figure 3–9 BDLC Multiple Outstanding Transactions
Another consideration is that of the six configurable modes described in
Chapter 2, two of those modes emulate the original TIWAY I Host Adapter,
meaning that they require the NITP protocol. If you plan to use either the
Master Host Interface Unit (MHIU) or Host Interface Unit (HIU) in EHA mode,
you must also use the NITP protocol because these modes do not support
commands for configuring network parameters and the dipswitch used to
define the BDLC address is used to define those network parameters.
Another factor to consider is the type of secondary devices that will be on your
network. If you will be connecting Computer Interface Modules (CIM) or
Intelligent Tank Transmitters (ITT) in CIM mode, you must configure the
adapter as an MHIU/EHA which requires the NITP protocol. ITTs may also be
used in the TIWAY mode without the above restriction.