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Slave Devices that Require Polling:
This configuration will also work with systems where the
devices have to be polled for information. With the setup of Figure
2.3, the switches can be configured so that you still only have to
send one set of switching characters. To do this, set the switches up
in the following way:
Set the switch on Level 1 to broadcast to all slaves on
startup.
Set the switch on Level 1 to Auto Select mode, no preamble.
Set the switch on Level 1 for 0 Port Time
Set the switch on Level 1 for a short Inactivity Time.
Somewhere around 5 milliseconds or so.
Set the switches on Level 2 for no Auto Select.
Set the command sequences on the Level 2 switches to be
unique from each other. One suggestion is to use a 3
character command. Use the first character as a start of
command character like STX. The second character could
represent the address of the Level 2 switch you are going to.
The third character is the command character.
Write the software to send the command to select the port.
By setting the Layer 1 switch to broadcast and Auto Select,
only 1 set of command characters is needed.
Cascading switches becomes more complicated when the devices
are a mix of polled and automatic sending of data. It is also difficult
to cascade when devices are streaming data constantly, or
automatically sending a variable length packet of data.
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B&B Electronics – Westlink Commercial Park – Oranmore, Galway, Ireland – Ph +353 91-792444 – Fax +353 91-792445 – www.bb-europe.com
Documentation Number 232BSS4-0812m
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