Siemens SIMATIC TIWAY 1 - Manual (Page 68)

CONFIGURING THE HOST COMPUTER PORT
UNILINK HOST ADAPTER 3–10
USER MANUAL
The BDLC protocol is a byte–oriented subset of the ANSI X3.66 standard
protocol, similar to the ISO standard HDLC protocol. The major features of the
BDLC protocol are listed below.
D It provides a higher level of data integrity and throughput
improvements over NITP, but it is also more complex to implement.
D It uses send and receive counts in a control field for improved data
integrity.
D Throughput is improved by transmitting the data as eight-bit binary
values or hexadecimal, making this protocol approximately twice as
fast as NITP. However, you will have to write and/or install the BDLC
protocol driver software on your host computer.
D Additional throughput improvements are gained by using the multiple
outstanding transaction capability, illustrated in Figure 3–9. This
allows the host computer applications software to continue issuing
commands before the network response is returned. The host computer
can issue a network request to secondary device #1, then another to
secondary device #2, followed by the command to retrieve the response
from secondary device #1.
D It uses an address to distinguish individual adapters in a multipoint
host interface circuit as described in Paragraph 3.2.3.
More detailed specifications are given in Appendix B.