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4-1SectionApplication Procedure
35
4-1-1 Host Link Communications
Host Link communications are supported by all CQM1H-series CPU Units. A
Serial Communications Board can be used to connect a single PC to more than
one host computer for Host Link communications, including slave-initiated com-
munications. Host Link communications provide the following features.
An RS-422A/485 port can be used to connect one host computer to up to 32
CQM1H-series PCs.
Host Link communications enable the host computer to monitor or control PC
operations and to read and write I/O memory in the PCs.
Both vertical and horizontal (FCS) parity checks are performed on communica-
tions data to achieve essentially error-free communications. Combining error
checking and retry processing goes one step further to eliminate nearly all the
effects of communications problems.
The Serial Communications Board provides two serial communications ports
that can be used simultaneously to connect to two different networks of host
computers in addition to the connections made directly from the built-in CPU
Unit ports.
Communications can be performed either by sending a command from a host
and having the PC return a response, or by sending data from a PC to the host.
Note A Host Link connection can also be used to connect the PC to a Programming
Device running on a personal computer. The following two modes can be used to
connect to computers running Programming Devices. Only the Host Link Mode
can be used for the Serial Communications Board.
Serial communications
mode
Features
Host Link Functions as a communications protocol with standard
host computers.
Either 1:1 or 1:N connections are possible.
Slower than a peripheral bus connection.
Connection is possible through a modem or Optical Link
Adapter, and long-distance and 1:N connections are
possible using RS-422A/485.
Peripheral bus Enables high-speed communications. A peripheral bus
connection is thus the normal mode used to connect to a
computer running the CX-Programmer.
Only 1:1 connections are possible.
With the CQM1H, the baud rate of the Programming
Device is detected when the connection is made.
Connect One Computer
to Multiple PCs
Computer Monitoring
and Control of PCs
Redundant Error
Checking
Simultaneous Usage of
Both Ports
Slave-initiated
Communications