ADLINK PCI-7856 - Manual (Page 27)

Motionnet Master-Slave Motion System 15
PCI-7856
User’s Manual
2. Minimum cable length 
The shortest cable must be at least 60 cm long.
3. Do not mix cables of different types and model in the
same serial line.
4. Keep the total serial line length as short as possible.
5. If you are using shielded cables, do not connect the
shield on both ends to the FG terminals. 
Connecting only one end of the shield on each cable will
improve noise immunity.
3.1.2 MNET System Communication
An MNET system communication block diagram is shown below.
Command Launching
Within the MNET system, remote modules communicate with
each other using MNET network packets. Users do not have to
understand what the content of the packet is. Instead, several API
functions are provided for controlling this module. The API func-
tions are very easy to understand and to use.
The APIs can analyze the parameters from user commands and
pack them as MNET network packets. The packets are then
passed to the remote modules. The remote modules will interpret
the packets and execute the commands correctly. Before launch-
ing the packet, all the commands issued by users are written into
the RAM and transferred on the MNET network.
Consequently, the RAM is the bridge between the MNET master
controller and the host PC. The access time of RAM for one
packet is about 600 ns. It is quiet fast on host PC. Furthermore,
the delivey time of one command on network depends on the
number of modules and operating clock rate. Besides the basically
Host
Motionnet
Bus
MNET Single
modules
Motion
Amp.
Command
Launching
Command Delivering Command Dispatching Command Executing