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6. Redundancy with NX3030 CPU

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Redundant and Non-redundant %Q Variables

The NX3030 CPU allocates 96kbytes of %Q variables (%QB0 ... %QB98303).

The first 80 Kbytes can be redundant (%QB0 ... %QB81919). The last 16kbytes are always non-

redundant (%QB81920 ... %QB98303).

The 80 Kbytes area which can be redundant is divided in two sections:

 The first Kbytes are reserved for outputs that can be redundant, and are typically allocated for an

I/O remote system (PROFIBUS, Modbus, etc.). The size value is configurable and its default

value is 16384. By default, this section includes %QB0 ... %QB65535.

 The next bytes are reserved for diagnostics which can be redundant, from the I/O system (I/O

modules diagnostics, communication interfaces diagnostics, PROFIBUS slaves diagnostics, etc.),

for instance. Different from the quick diagnostics (allocated in %I), such diagnostics allocated in

%Q can take more than one MainTask cycle to be updated. By default this section includes 16

Kbytes (%QB65536 ... %QB81919).

The non-redundant area (%QB94208 ... %QB98303) is typically allocated for diagnostics and private

commands of a half-cluster, and also for the redundancy command panel PX2612 LEDs and relay.

The user can reduce the redundant %Q variable quantity in each one of the sections which can be

redundant…

 On the first section, the really redundant area size can be configured between 0kbytes and 65535

bytes, in 1kbyte multiples (the default value is 16384 bytes). The proper configuration of

redundant %Q is important to decrease the necessary time for redundant variables

synchronization (decrease the redundancy overhead). E.g. if the real application allocates only

%Q0 ... %Q1499 for redundant outputs, the redundant %Q area size can be defined as 1500

bytes.

 On the second section, the really redundant area size can be configured between 0kbytes and

81919 bytes, in 1kbyte multiples (the default value is 16384 bytes). The proper configuration of

redundant %Q is important to decrease the necessary time for redundant variables

synchronization (decrease the redundancy overhead). E.g. if the real application allocates only

%QB65536 ... %QB66999 for redundant diagnostics, the redundant %Q area size can be defined

as 1464 bytes.

The figure below illustrates the redundant and non-redundant %Q direct representation variables

allocation, where RQS is the %Q output quantity configured as redundant in the first section, and

RQD is the %Q diagnostics quantity configured as redundant in the second section.

ALTUS Nexto NX3004 User Manual

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